Abdur Rahman bin Ishaq عبد الرحمن بن إسحاق بن عبد الله · The Book on Jana''iz (Funerals)

The Prophet was brought a (deceased) man to perform Salat over. So the Prophet said: "Pray for your companion; for indeed he had a debt upon him." Abu Qatadah said: "It shall be upon me." So the Messenger of Allah said: "To pay it off?" (He said: "To pay it off.") So he performed the prayer for him.