Sastiel

"The answer is still no, because Sam is my friend."

- Castiel to Anna; The Song Remains the Same

Sastiel is the slash ship between Sam Winchester and Castiel from the Supernatural fandom.

Canon
Castiel and Sam don't meet for a while, but they are both aware of each other's existence. Sam hears about Castiel from Dean. Castiel knew about Sam, and the fact that Sam was using his powers to exorcise demons with his mind. Sam does want to meet Castiel, mainly because he wants to thank the angel who saved his brother. The two do finally meet face to face in It's the Great Pumpkin, Sam Winchester.

S4 =

It's the Great Pumpkin, Sam Winchester
Sam enters the motel room, when he sees a man and pulls out his gun. Dean stops him, explaining that it's Castiel. Castiel says hello to Sam, who become's excited, saying oh my god, before quickly becoming awkward. He attempts to shake Castiel's hand, and after a moment Castiel takes it. He says it's good to meet him as well, and that the's glad that Sam stopped using the demon blood powers. Uriel says to keep it that way, and Dean asks Castiel who his friend is. Castiel instead asks if witch trying to raise Samhain is dead, Sam saying no. Castiel tells them that the witch knows who they are, and shows them the hex bag that was in the wall of their room. If they hadn't found it, they would be dead. Castiel asks if they know where the witch is now. Castiel tells them that Samhain is one of the seals, that it has to be prevented. Castiel tells them that they can't find the witch and Sam says that since they know who she is they can work together to find her but Uriel interrupts them. Castiel tells them that they need to leave town, since they're about to destroy it. Sam says that there are 1000 people in the town and asks if they're really willing to kill them all. Castiel says that it's regretabble but there's already been too many broken seals. Castiel says that they have their orders, Sam says that they can stop Samhain from being freed. They're angels and are supposed to show mercy. Castiel says that they have no choice. Sam asks how he can say that and Castiel says that if it comes from heaven the order is justified. Dean is able to convince them to let them try and stop the witch themselves.

Sam once saved Castiel from Alastair when the latter was about to kill him as Castiel was amazed by Sam's power when he killed the demon.

On The Head Of A Pin
Castiel comes to Dean's hospital, where Sam is sitting beside his brother's bedside. Sam demands Castiel gets in there and heal Dean. Castiel tells Sam he can't. Sam argues that Cass and Uriel are the ones who put Dean in there, all because they can't keep a simple devil's trap together. Castiel apologizes to Sam, unable to explain what happened. Sam snaps at Castiel, saying that making Dean torture again was for nothing. It's not the demons, but something else. Castiel brings up the possibility that Alastair was lying, but Sam shoots it down. Castiel believes Sam is right about this.

Just as Alastair performs the ritual to send Cas back to heaven, he's pushed to the side by Sam using his powers. As Sam interrogates Alastair, Castiel watches. When it's revealed that the Demon's aren't the one's killing the angels, Alastair dares Sam to send him back to hell. Sam reveals that he can kill demons now, much to Cas' shock. Sam and Cas look to each other.

Sam sits by Dean side at the hospital, Cas walking by the room and watching the two. Sam sees Cas, and he walks slightly away, Sam following him. Sam tells Cas to heal Dean, but Cas says that he can't. Sam says that his fault, and Cas says that he doesn't know what went wrong, the trap shouldn't have broken, and he apologizes. Sam calls the whole thing pointless, since the demons aren't killing the angels. Cas suggests that Alastair was lying, but Sam knows that he wasn't. Sam then walks away, and back into the hospital room.


 * -|S5 =

Sympathy for the Devil
As Zachariah tortures Sam and Dean, Cas suddenly appears and kills one of the angels. He fights off the other angel. Cas asks Zachariah how Dean and Sam got on the airplane, if it wasn't the angels. He demands that he fix Sam and Dean, then leave. Zachariah leaves, and Sam and Dean get up from the ground. Cas tells them that they need to be more careful, Dean agrees. Cas says he doesn't mean the angels, but Lucifer. He looks between Sam and Dean and touches their chests, carving enochian sigils to hide them from the angels. Sam asks Cas if he was really dead, and Cas confirms so. Dean asks how he got back but he doesn't give an answer.

I Believe The Children Are Our Future
Dean and Sam arrive back at their hotel room where they find Cas. Sam guesses that he got their message, and Cas tells them that they're lucky they found him. Dean asks what they do with him, and Cas tells them to kill him, shocking Dean and Sam. Cas reveals that Jesse is actually the anti-christ. Sam is confused since he thought the antichrist was the son of Lucifer, but Cas tells them that it's just the child of a demon, but he is one of Lucifer's weapons. Sam tells him that they're not going to kill a child. Cas reminds him that he would have done whatever to stop the war a year ago, but Sam says that things change. They stare at each other till Dean steps in and tells Cas that they won't kill him, but they can't leave him either so they'll take him to Bobby's and figure it out from there. Cas tells him that this is what Jesse is like when he's happy, it'll be so much worse if it's angry, and starts pointing out the holes in their plan. Sam decides that they'll tell Jesse the truth and stop him from going darkside, but Cas reminds Sam that even when he had everything layed out, he made the wrong choice. He can't take the chance and leaves.

Sam and Dean find Jesse's room empty, and Cas come up and tells him that he's gone and turned everyone back to normal. Dean asks how they'll find him, but Cas says that they can't, unless he wants to be.

The Song Remains the Same
Cas works on a spell as he tells Sam and Dean about Anna. Sam asks if Anna's plan will stop Lucifer, but Cas assures him that it wouldn't. Dean asks why they're trying to find Anna, and he explains that Anna won't stop till Sam is dead, so they need to kill her first. He performs the spell and finds out that she's in 1978. Sam asks why, since he wasn't born yet. Cas says that she's going to kill John and Mary, since she can't get to Sam because of him. Dean tells him to take them back, but Cas says no. Dean insists since it's their parents, but Cas says that'd it's now more difficult since he's cut off from heaven. Cas says that the trip will weaken him, but Dean still insists and Cas gives in. They pack and he asks if they're both ready. Sam says not really, and they go back to 1978.

99 Problems
When Sam figures something is not right in a town, he calls Castiel in for help. When Castiel shows up drunk, he tells Sam he finds his voice grating. Sam notices Castiel is drunk and asks what happened to Castiel. Castiel answers he found a liquor store and "drank it". Sam attempts to help Castiel from wobbling, and asks if he's okay. Castiel leans over and tells Sam not to ask stupid questions. Sam tells Castiel about the demon attacks around town and the "prophet" Leah Giden. Castiel tells Sam that she is no prophet (because all the names of the prophets are seared into Castiel's brain), and then Sam asks then what Leah is. Castiel later reveal that "Leah" is actually the Whore of Babylon. When Castiel brings a weapon to kill her, he tells them that only a true servant of God can use it to kill her. Castiel continues on by saying he can't do it, and, neither can Sam since he's an abomination (because of the demon blood). Sam looks slightly hurt, but understands. When Dean decides to say 'yes' to Michael in Point of No Return, Sam brings Castiel along to help him stop Dean. Castiel uses his powers to send Dean to Bobby's house. Like Sam, Castiel is angry at Dean for giving up, so they both work together to make sure Dean doesn't leave Bobby's. When Dean does escape, Castiel brings Dean back unconscious. Sam asks Castiel what happened and Castiel answers "Me". Later on, Sam decides to bring Dean along on a mission, despite Castiel not wanting to Dean to come along. Castiel can't understand Sam's blind faith in Dean.

As the final showdown comes along, Castiel comes once again to aid the Winchesters. In Two Minutes to Midnight, Castiel saves Sam from being strangled to death. Castiel is amazed how useful guns can be. Then in Swan Song, Castiel says an awkward goodbye to Sam, as Sam prepares to have an internal battle with Lucifer in his head.

After Sam trapped Lucifer and Michael into hell (at the cost of himself), Castiel who was resurrected and promoted to Seraphim used his new powers to successfully raise Sam from Lucifer's cage. Unfortunately, Sam's soul was left in the cage.

After Sam returned from hell, he called Castiel many times, but Castiel never answered, so Sam stopped calling. In The Third Man Sam tells Dean that Castiel won't answer, but when Dean calls Castiel, he appears, which surprises Sam, who mocks Castiel's "Hello". Sam continues by saying that he's been calling Castiel all this time and Castiel only comes when Dean calls him. Sam continues by asking if Castiel likes Dean more. Castiel answers by saying he and Dean share a more profound bond. Castiel also tells Sam he has no idea who brought Sam back from the cage, or why. When Sam tries to get more information, Castiel angrily replies "What part of I don't know escapes your understanding?" Later on in a fight with another angel, Castiel destroys Sam's car.
 * -|S6 =

In Family Matters, Castiel is trying to figure out what is wrong with Sam. Castiel starts asking Sam questions, and finishes with asking how Sam feels emotionally. Sam answers he doesn't know. Castiel tries to feel Sam's soul, only to find out Sam doesn't have one. Sam looks shocked at this discovery. Castiel tells Dean whoever brought Sam back, left his soul behind. When Dean asks if "Sam" is still even Sam, Castiel answers that it is an interesting philosophical question.

Castiel continues to help in the quest for Sam's soul in Caged Heat. Although he doesn't come right away. Sam tricks Castiel into coming down and calls Castiel an idiot for believing his lie. Sam asks Castiel to help, but Castiel refuses (due to the civil war). Sam continues by saying Castiel owes him and if Castiel doesn't help, Sam will find a way to kill Castiel (pointing out the extra time to do so since Soulless Sam doesn't sleep). So Castiel agrees to help. Later on, Castiel seemingly threatens Crowley to get Sam's soul back, but when Crowley says he can't, Castiel toasts Crowley's bones. Castiel reassures Sam they will find another way to get Sam's soul back.

In Like A Virgin, Sam now has his soul and Dean calls Castiel to check on Sam. Castiel tells Dean that Sam's soul felt like it had been skinned alive. Later on in the episode, Sam calls Castiel. Castiel tells Sam its good to see him alive and attempts to hug Sam (who sits down to avoid it). Sam tells Castiel he would hug Castiel, but it would be awkward. Sam goes on to talk about how its been a crazy year and how he just talked to Bobby about it. Castiel tells Sam he's surprised Sam even survived. Castiel asks Sam how it feels. Sam looks confused. Castiel explains, "to have your soul back". Sam is shocked to hear this news and plays along so he can get more details from Castiel about what really happened. After hunting Eve down, Sam (plus Bobby) begin to have suspicions about Castiel. Sam starts not to trust Castiel, and believes him to be working with Crowley (The Man Who Would Be King). Castiel still protects Sam and Dean despite these doubts. Then when Castiel's betrayal comes to light, they trap Castiel in a ring of holy fire. In there, Castiel tries to maintain his loyalty to them even revealing that he was the one who brought Sam back from the cage. Though surprised, Sam asks Castiel if he meant to bring Sam back soulless. Castiel tells Sam he didn't mean to (he didn't even know until Family Matters).

Despite Castiel's betrayal, Sam wants to call and does call Castiel for help in Let It Bleed. Although Castiel doesn't show himself, he answers Sam's prayer. Then Castiel does the unthinkable in The Man Who Knew Too Much. In order to detour Dean, he breaks down the wall inside Sam's mind and Sam goes into a coma. Castiel says he'll save Sam, only if they back off. Sam does wake from his coma, and comes to Dean's rescue. Sam stabs Castiel only to find out that Angel Blade doesn't work on him.

Even after Castiel tore down his wall, Sam still believes that they can reach him. Despite Dean thinking Castiel won't listen, Sam calls Castiel, and tells him they can help. Although Castiel doesn't answer right away, he comes to Sam's call and asks for help. Sam sets out with the others to help Castiel.
 * -|S7 =

The last moment they have together is when Castiel tells Sam where to find the blood cocktail meant to open Purgatory. Later, Castiel is overcome by the Leviathans, and Sam watches Castiel disappear into the water.

In The Born-Again Identity, Castiel comes to Sam's rescue as a demon attempts to fry Sam's brain. Castiel attempts to right his wrong by attempting to fix Sam's mental state, but fails. Castiel deeply regrets what he did to Sam, and he states that he can't fix it. Then the idea hits Castiel to switch places with Sam's mental state. Castiel takes on Sam's insanity, and begins to see Lucifer. Now sane, Sam is shocked to see Castiel alive, and becomes worried about how he's acting. Sam is a bit shocked that Dean wants to leave Castiel in the mental institution.

In Reading Is Fundamental, Sam thanks Castiel for helping him and taking on his hell. Sam promises to help find a cure for what Castiel took on. Castiel tells Sam that he doesn't need to fix anything and that taking on Sam's pain gave him purpose. Castiel also mentions that he doesn't see Lucifer anymore since it was Sam's own hallucination. Sam is sad to hear Castiel doesn't think that he's broken.

Sam inquired about what happened to Castiel in Purgatory, but got no answer from Dean. Sam is excited to see Castiel's return and is less suspicious of it than Dean.
 * -|S8 =

In A Little Slice of Kevin, Sam is surprised to see Castiel, but is happy to see an old friend. He later offers Castiel to join them in hunting down The Word of God, something Castiel accepts.

In Hunteri Heroici, Sam and Castiel make a connection when Sam is talking about living in a dream. When Castiel brings himself and Sam into the mind of Fred Jones, Castiel can relate to Sam, as he too, has been running from his problems, and makes a decision to return to Heaven, but is shot down by Naomi. In Clip Show, when Castiel's relationship with Dean is strained due to Dean's anger over Castiel's lack of trust in him, Sam comforts Castiel, trying to convince him that Dean just needs time.

In "I Think I'm Gonna Like It Here," Castiel agrees to stop helping Hael in order to come and save Sam when he's dying. He also gives Dean his approval of Ezekiel helping, saying Ezekiel is a good soldier and indicating they are friends.
 * -|S9 =

In "I'm No Angel," When Castiel is being tortured by the Reaper possessing April Kelly, Sam comes to his rescue with Dean though Castiel is briefly killed. Afterwards, Castiel is excited by the idea of Sam and Dean being his guides to being human, but Dean is forced to ask him to leave to save Sam who "Ezekiel" threatens to leave and let die if Castiel doesn't go.

In "Holy Terror," Castiel works a case of angel deaths with Sam and Dean, but "Ezekiel" once again forces Dean to send him away. However, this time, Dean partially explains why to Castiel who continues investigating on his own. After learning from Malachi that Ezekiel is dead, Castiel escapes and calls Dean to warn him that the angel who helped Sam isn't really Ezekiel. Unfortunately, his warning comes too late.

In "Road Trip", after the angel possessing Sam kills Kevin and takes off, Castiel comes to aid Dean with saving him. While Dean is originally going to kill Sam to kill the angel, Castiel presents the solution of going to Crowley for help to get him to do what he did with Samandriel to bring out Sam and get him to expel the angel. After finding "Sam", Castiel knocks him out and watches as Crowley tortures the angel to get information, admitting to Dean that its not easy for him to watch. He is also able to confirm that the angel did in fact heal most of the damage to Sam's body from the Trials. Castiel is furious to learn that the angel is actually Gadreel, the angel that allowed evil into the Garden of Eden and thus started all of the chaos on Earth. Dean eventually asks Castiel to possess Sam to help him force Gadreel out, but Castiel can't do that as he needs Sam's permission. However, Crowley can so at Dean's request, Castiel removes Sam's Devil's Trap Tattoo so Crowley can possess him. While waiting to see if it will work, Castiel reassures Dean. Finally, with Crowley's help, Sam expels Gadreel and Castiel heals the wounds he got from the torture, promising to finish Gadreel's healing of him though it will take time. When Dean leaves, Castiel stays with Sam.

In "First Born," Castiel stays with Sam in the bunker, trying to enjoy human things such as a sandwich but having a hard time as an angel. He also pushes him to make up with Dean. Castiel has nearly finished healing Sam and when he goes to give him his next treatment, he discovers that Sam still has some of Gadreel's grace inside him. Castiel discovers that they can use the residual grace to track Gadreel from the Men of Letters files and painfully starts extracting the grace from Sam. Castiel soon discovers that losing the grace is causing Sam to start to revert to the state he was in before Gadreel possessed him, but Sam insists they keep going as he wants to make up for his past which Castiel reluctantly agrees to. Eventually Sam's condition deteriorates badly and Castiel chooses to finish healing him completely, destroying the rest of the grace rather than sacrifice Sam even though they might not have enough grace for the spell. Castiel explains that being human has taught him that he was wrong in the past about doing whatever it takes to achieve what he wants and that he empathizes with Sam as he is the only one who has screwed up more times than Sam has. With this, Castiel officially loses any remaining disgust he holds towards Sam and his nature. After the spell fails, an appreciative Sam gives a stunned Castiel a hug and he returns it.

Following the defeat of Metatron, Castiel begins gathering rogue angels. Sam eventually calls to tell him that Dean is a demon, much to Castiel's discomfort. After Crowley provides Castiel with extra grace, Castiel rushes to the bunker to rescue Sam from a murderous Dean Winchester.
 * -|S10 =

When Sam begins a plan to remove the Mark of Cain from Dean, he allows Castiel to help him. The two keep this mission a secret, and go as far as to recruit the help of Bobby Singer, Charlie, and Rowena.

Castiel goes to Heaven to meet Bobby and retrieve Metatron, who is believed to know a cure for the Mark. Upon his return, Castiel delivers a letter from Bobby to Sam. When Rowena and Charlie are asked to help, Castiel is tasked with guarding the witch to ensure Charlie is comfortable.

Some time after The Darkness was released, Sam is reunited with a sick Castiel and helps the angel search for his "crappy" car. When the spell cast upon Castiel takes over, Sam is the one to point a gun at Rowena's head to make her undo the spell. Afterwards, Sam joins Dean in insisting that Castiel rests, and in "Baby", Sam introduces Castiel to Netflix.
 * -|S11 =

When Sam ends up trapped inside a cage with Lucifer in "The Devil in the Details", both Castiel and Dean rush to help him fend off the archangel. All three seemingly escape unchanged.

In "The Vessel," when Dean gets left behind on the USS Bluefin due to warding sigils, Sam works with "Castiel' to find a way to bring him back. Sam offers the use of his soul to power a spell that can remove the wardings on the submarine, but Sam soon discovers that "Castiel" is in fact Lucifer.

Lucifer takes Sam upon his offer and proceeds to penetrate his chest, causing Sam immense pain. Before Lucifer can do any serious damage, Castiel uses every ounce of his strength to regain control of his vessel and save Sam. Although Castiel is forced to surrender control back to Lucifer so the archangel can rescue Dean, Castiel was able to keep Sam out of harm's way.

However, the revelation that Castiel said "yes" convinces Sam that Castiel wants to be a vessel, and thus does not wish to be saved. Dean persistently argues that this is not the case, and Sam, hoping his own beliefs are untrue, has assisted in every attempt made to rescue Castiel.

Sam and Castiel are reunited after a botched fight against Amara ends with Lucifer expelled from his vessel. When Dean prepares to confront Amara in their latest plan, Castiel promises Dean that he will watch out for Sam and make sure he doesn't do anything stupid. Sam and Castiel later gather at a bar with Crowley, Rowena and God.

When Dean's mission appears successful, Castiel follows Sam back to the bunker, but is suddenly banished by a blonde woman.

Castiel returns to the bunker only to find Dean and a resurrected Mary Winchester. The three decide to rescue Sam from the blonde woman. The confrontation leads to a success and Sam is brought back home in "Mamma Mia".
 * -|S12 =

Knowing Lucifer is still on the loose, Castiel leaves the bunker alone to deal with the archangel, whose freedom he blames on himself. Sam and Dean do not get involved in Castiel's hunt until "Rock Never Dies", when the trio, plus Crowley, track down Lucifer to Los Angeles. The four manage to prevent Lucifer's plan to murder a dozen human who are attending a concert he hosted under the guise of his vessel, Vince Vincente.

Lucifer escapes capture, however, the four continue hunting down the archangel as he takes on various vessels, until he reaches President Jefferson Rooney. As soon as Castiel senses it, he quickly informs Sam and Dean that Lucifer has now conceived a child. The gang make a plan to confront Lucifer's mistress and convince her to abort the child. On their way, the US Secret Service block their path and nearly arrest Sam, Dean and Castiel until Arthur Ketch, an associate of Toni Bevell, arrives and knocks the agents out.

Ketch offers them a weapon to expel Lucifer from the President; with Rowena in tow, the gang are successful in freeing the President from possession. Castiel leaves the area with Lucifer's mistress Kelly, while Crowley takes Rowena away, leaving the brothers unintentionally at the mercy of the US Secret Service, who arrive and arrest Sam and Dean for trying to assassinate the President.

Castiel tries to convince Kelly himself to abort the child she is carrying. To his horror, Kelly accepts that Lucifer is the child's father but runs away instead of aborting it. Unable to find her, Castiel waits at the bunker for Sam and Dean's return, but to his misery, the brothers do not return. Castiel and Mary seek out help from Arthur and Arthur's associate, Mick Davies, and the men are able to locate Sam and Dean at a secret prison called Site 94. Once there, Castiel is tearfully reunited with the brothers, but their happiness is short-lived when Castiel and Mary learn that Sam and Dean had offered their lives up to Billie in exchange for escaping the prison. When Mary offers himself up instead of her sons, an unwilling Castiel refuses to let any of the Winchesters die, as a result he kills Billie and reprimands the brothers for even thinking that this world doesn't need them. He declares that he will not let them sacrifice themselves as they are important to him and he'll deal with the consequences of their acts.

The three are very surprised by Castiel's actions and care for them and go back home to the bunker.

When the Nephilim was about to be born, Castiel briefly betrayed the Winchesters as he saw the good in the unborn infant. Sam and his family track down Cass and tell him to regain his sense of mind before he shows them Apocalypse World and they have to fight Lucifer. Once the archangel is sent to the other realm, Castiel arrives to stab him as Sam tries to warn him to no avail. However, when he returns to the main reality, Sam is briefly relieved until Lucifer stabs and kills Castiel, with Sam left devastated at the corpse of his close friend's lifeless vessel.

In Lost & Found, alongside Jack, who sees Castiel as his father instead of Lucifer, the Winchesters burn Castiel and Kelly Kline's bodies outside the cabin.
 * -|S13 =

During Patience, Sam shows that he doesn't put Castiel's death on Jack's hands. Though it is clear, he does miss his friend.

In The Big Empty, after awakening in The Empty, Castiel tells the Cosmic Entity that the Winchesters need him and demand for his release as he will fight it for all eternity if he has to until he is freed from the realm. At the end, Castiel is resurrected just as he demanded.

During Advanced Thanatology, Castiel calls Dean from a service phone, as a sleeping Sam wakes up questioning his brother who is shocked. The brothers drove to a small town where they find Castiel standing by a payphone and are shocked to see him alive again.

At the beginning of Tombstone, the brothers question how Castiel can be alive as he explains that he was resurrected by the Cosmic Entity. Sam asked if Castiel was sent to Heaven but he tells them that he was put in The Empty as he describes his horrible experience in the void of nothingness. Sam even deduced that Jack had a part in bringing Castiel back before he embraces Castiel after confirming that his friend has truly returned.

Season 4
I Know What You Did Last Summer
 * Sam asks Castiel if they're there to help Anna.

Heaven and Hell
 * Sam asks Castiel why they want Anna.
 * Sam yells that Anna is an innocent girl, but Castiel says that she’s far from innocent.
 * Castiel makes his way to Anna, Sam walking in front of him and telling him to stop, but Castiel just knocks him out.
 * Sam asks how they found them, and everyone feels awkward till Sam realizes that it was Dean.
 * Sam and Dean watch as Castiel tries to smite Alastair.

Death Takes a Holiday
 * Cas tells Dean that he and Sam stopped one of the seals from being broken.
 * Castiel reveals that he's the one that called Sam about the job.

On The Head of a Pin
 * Sam and Dean see Castiel and Uriel when they enter their hotel room.
 * Castiel looks to Sam and Dean.
 * Cas tells Uriel what Sam told him.

The Monster at the End of this Book
 * Dean tells Sam that Cas told him about Alastair.

 The Rapture 
 * Sam asks Dean what Cas wanted that was so important.
 * Sam asks if Cas was fighting angel.
 * Sam heads toward Cas and calls his name.
 * Sam tells Cas to take it easy.
 * Sam tells Jimmy that Cas wanted to tell him something and asks if he remembers.
 * Sam suggests that Cas might repossess Jimmy.
 * Anna tells Sam and Dean that Cas got dragged back to Heaven.
 * Cas and Dean watch Sam drink demon blood and excorcise one of the demons.
 * Dean and Sam watch Cas switch vessels from Claire to Jimmy and walk away from Amelia and Claire.
 * Sam watches Cas leave.

When the Levee Breaks
 * Dean calls Cas about Sam.
 * Castiel lets Sam out of the safe room.
 * Castiel watches Sam head up the stairs.

Lucifer Rising
 * Cas stops Dean from going to Sam.
 * Cas tells Dean to go save Sam.

Season 5
Sympathy for the Devil
 * Sam points out a Cas' tooth still stuck in Chuck's hair. Dean calls Cas a stupid bastard, Sam reminding him that he was trying to help them, but Dean says that's the point.

Good God, Y'all
 * Dean shows Sam the X-Ray of his lungs that Cas.
 * Sam answers a call from Cas. Sam tells him where they are, and Cas hangs up, confusing Sam and Dean.
 * Cas stands between Sam and Dean.
 * Sam watches Dean and Cas talk.
 * Cas says that there is still someone strong enough to take on Lucifer, and Sam asks who. Cas tells him god, surprising both Sam and Dean.

Free to be You and Me
 * Cas asks Dean where Sam is.
 * Cas asks Dean if he's okay without Sam.

I Believe The Children Are Our Future
 * Sam holds the Cas doll.

Changing Channels
 * Sam asks if Cas being there is a trick, but Sam says that it's real.
 * Cas tries to get Sam and Dean out of TV land, but Gabriel stops him.
 * Sam asks Cas what happened, and Cas says he got out.
 * Sam asks Cas what he means about the trickster.
 * Sam asks if Gabriel knows Cas.
 * Sam reminds Dean that Cas said that he was to be powerful to be a trickster.
 * When Gabriel asks where he screwed up, Sam says that he didn't, but nobody gets a jump on Cas.
 * Cas joins Sam and Dean outside.

Abandon All Hope
 * Sam puts his arm over Cas' shoulder.
 * Ellen asks Sam and Dean if they've seen Cas.
 * Cas tells Lucifer that he's not taking Sam.
 * Sam asks Dean if he thinks Lucifer took Cas.

Sam, Interupted
 * Sam mentions Cas to the doctor.

The Song Remains the Same
 * Cas tells Anna that Satan would just bring Sam back if she kills him.
 * Cas says that they answer is no, Sam is his friend.
 * Cas Anna that if she comes near Sam, he will kill her.
 * Sam and Dean find Cas injured and rush to him.
 * Sam checks that he's breathing, and asks what they do.
 * Sam asks if Cas is okay, and Dean says that he doesn't know.
 * Sam and Dean are getting ready to leave in the motel room, when Cas appears. He starts to fall and Sam catches him.
 * Cas looks from Dean to Sam.
 * Sam and Dean drag a passed out Cas to the bed.

Quotes
"I was lost until I took on your pain."

- Cas to Sam; Reading Is Fundamental.

"Nothing is worth losing you."

- First Born.

Fanon
Sastiel has a very dedicated fan base. It's not considered the top ship in the fandom but is still pretty common.

On AO3, Sastiel is the second most written ship for Castiel and the fourth most written relationship for Sam. It's also the eighth most written ship in the Supernatural tag.

Fandom
FAN FICTION
 * Sam/Castiel on FanFiction.Net
 * Sam/Castiel on FanFiction.Net

TUMBLR

Trivia

 * In Red Sky At Morning, one of the names that Sam reads for a spell is Castiel.
 * In Appointment In Samarra, Balthazar jokingly called Castiel Sam's boyfriend.
 * In Fan Fiction, Sam joked about naming his and Castiel's ship name "Sastiel" or "Samstiel" after hearing about Destiel.

Variations

 * Mishalecki refers to the ship between their actors; Misha Collins and Jared Padalecki
 * Team Free Will refers to the ship between Sam, Dean Winchester and Castiel