Musannaf Ibn Abi Shayba 13:1631

Abu Bakr narrated to us, he said: Abu Khalid al-Ahmar narrated to us, from Isma'il ibn Abi Khalid, from al-Sha'bi, from 'Ubaydah, from 'Ali, who said: 'Umar consulted me regarding the selling of the *ummahat al-awlad* (slave women who have borne children to their masters). I and he were of the opinion that if she gives birth, she is emancipated. 'Umar judged by this during his lifetime, and 'Uthman after him. When I assumed authority after them, I saw that I should keep them in servitude. Al-Sha'bi said: Ibn Sirin narrated to me, he said: I said to 'Ubaydah, "What is your opinion?" He said: "The opinion of 'Umar and 'Ali in consensus is more beloved to me than the opinion of 'Ali when the disagreement was reached."