Harry Potter and the Prisoner of Azkaban, Chapter Nineteen
↳ The Servant of Lord Voldemort
"Remus!" Pettigrew squeaked, turning to Lupin instead, writhing imploringly in front of him. "You don’t believe this… Wouldn’t Sirius have told you they’d changed the plan?"
"Not if he thought I was the spy, Peter," said Lupin. "I assume that’s why you didn’t tell me, Sirius?" he said casually over Pettigrew’s head.
"Forgive me, Remus," said Black.
"Not at all, Padfoot, old friend," said Lupin, who was now rolling up his sleeves. "And will you, in turn, forgive me for believing you were the spy?”
"Of course," said Black, and the ghost of a grin flitted across his gaunt face.