Musannaf Ibn Abi Shayba 13:3387

Abu Bakr narrated to us, he said: Hushaym narrated to us, from Mughira, that a man said to his slave, "You are for Allah." He said: So al-Sha'bi, al-Musayyab ibn Rafi', and Hammad ibn Sulayman were asked, and they said: "He is free."