Musannaf Ibn Abi Shayba 13:1638

Abu Bakr narrated to us, he said: Husayn bin Ali narrated to us, from Za'idah, from 'Amr bin Qays, from Zayd bin Wahb, from Abdullah, that the sale of *umm al-walad* (slave women who have borne children to their masters) was mentioned to him. He said: "But Umar, the strong, the trustworthy, emancipated them."