Sahih Muslim Book 9, Hadith Number 3606.

Chapter: Excellence of securing the emancipation of father.

Abu Huraira (Allah be pleased with him) reported Allah’s Messenger (may peace be upon him) as saying: A son does not repay what he owes his father unless he buys him (the father) in case he is a slave and then emancipates him. In the narration transmitted by Ibn Abu Shaiba there is a slight change of words.