Musannaf Ibn Abi Shayba 26:490

Hushaym narrated to us, from Mughirah, from Ibrahim, who said: I asked him about a man who emancipated a slave of his, then he (the slave) died, and the master (who emancipated him) died, and he (the master) left behind his father and his son. Ibrahim said: For his father is one-sixth, and what remains is for his son.