You have it Imp, it was Sam. It was when they were all trying to get back to the wall and Sam thinks he's going to die from the cold and weariness. He thinks
"It will be warm under the snow, and if they speak of me they’ll have to say I died a man of the Night’s Watch. I did. I did. I did my duty. No one can say I forswore myself. I’m fat and I’m weak and I’m craven, but I did my duty."
Very shortly afterwards, he becomes Sam the Slayer!
Your turn, Imp.