Peter rebukes Tash and sends him packing with what is probably the Narnian version of "The power of Christ compels you!".
Then Tash turned his head sidewise to fix Tirian with one of his terrible eyes [...] But immediately, from behind Tash, strong and calm as the summer sea, a voice said:
"Begone, Monster, and take your lawful prey to your own place: in the name of Aslan and Aslan's great Father the Emperor-over-the-Sea."
The hideous creature vanished, with the Tarkaan still under its arm.