Ibn Jurayj (may Allah have mercy on him) said: I said to Ata' (may Allah have mercy on him): A mukatab had a slave, and he made a contract of manumission with him. Then he died; to whom does his inheritance go? He said: Those before (you) used to say: It belongs to the one who made the contract with him, who uses it to help pay his own contract.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21719