Musannaf Ibn Abi Shayba 13:400

Waki’ narrated to us, from Sufyan, from Mansur, from Ibrahim, from Alqama, who said: A man came to Abdullah and said: "My slave girl has breastfed my son; shall I sell her?" Abdullah said: "I wish he would take her out to the market and say: 'Who will buy my *umm al-walad* (mother of my child) from me?'" It was as if he disliked it.