Musannaf Ibn Abi Shayba 13:1639

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Isma’il bin Abi Khalid narrated to us, from ‘Amir, he said: ‘Uthman judged regarding the *umm al-walad* (a slave woman who has borne a child to her master) that she is free when she gives birth from her master.