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.
Jami` at-Tirmidhi Book 10, Hadith 105
← Previous Hadith "A man killed himself, so the Prophet did not perform Salat over him."

Jami` at-Tirmidhi Book 10, Hadith 104 Next Hadith → "A deceased man would be brought to the Messenger of Allah while a debt was due upon him. So he would say: 'Has he left anything to pay off his debt?' If he was told that he had left something to pay it then he would pray (the funeral prayer) for him. Otherwise he would tell the Muslims: 'Pray for your companion.' So when Allah granted him the victories, he stood and said: 'I am more worthy in the case of the believers than they themselves are. So whoever among the believers dies and leaves a debt behind, then it is up to me to fulfill it. And whoever leaves wealth behind, then it is for his heirs.'"

Jami` at-Tirmidhi Book 10, Hadith 106