Musannaf Ibn Abi Shayba 18:606

Abu Bakr narrated to us, he said: Hafs narrated to us, from Ash'ath, from al-Hakam and Hammad, from Ibrahim, who said: If a *mudabbar* (a slave promised freedom upon his master's death) kills someone or gouges out an eye, it is said to his master: "Hand him over, or pay his blood money (ransom)."