Episode 90 of "Angel"
s05e02 Just Rewards (2/2)

...Although Spike's body was destroyed in Sunnydale, his non-corporeal spirit has been sent back to the mortal coil against his will. Everyone tries to figure out what is going on while Angel is having trouble with a Necromancer named Hainsley. He is charging Demons for putting their essence into fresh corpses, which he is buying from Wolfram & Hart. After Hainsley kills the first messenger, Angel decides to pay him a visit to tell him that they will no longer supply him with bodies. Spike decides to tag along and is offered a body by Hainsley if he helps him. Angel learns that he cannot touch Hainsley, because he is being controlled by him. Angel and Spike argue about their souls, which leads Spike to make a decision. He tells Hainsley he will help him, but then jumps inside him. This allows Angel to hit him and finally kill him through decapitation. Spike jumps back out of his body and explains that Hainsley was dead way before the decapitation, but Spike wanted a few punches. Later on in Fred's office, Spike reveals that everytime he vanishes temporarily he is one step closer to falling into hell.. And he is terrified.