Musannaf Ibn Abi Shayba 13:1615

Abu Bakr narrated to us, he said: Abd al-Salam ibn Harb narrated to us, from Mughira, from Ibrahim and Amir, regarding the man who marries a slave woman, then she bears a child for him, then he purchases her. They both said: He may sell her as long as she has not borne a child while in his ownership.