Musannaf Ibn Abi Shayba 18:478

Abu Bakr narrated to us, he said: Zayd ibn al-Hubab narrated to us, from Hammad ibn Salamah, from Ibrahim, regarding a slave who killed a free man and was handed over to his (the victim's) guardians: He said: If they pardon him, he returns to his master, and they do not have the right to use him for service. Waki' said: And it is the opinion of Sufyan.