Musannaf Ibn Abi Shayba 9:216

Khalid ibn Habban narrated to us, from Ja'far ibn Burqan, who said: I asked al-Zuhri about a man who had a slave woman under him [as a wife], then he purchased her. He said: "The purchase annuls the marriage." Ja'far said: And I asked Maymun ibn Mihran about that. He said: "She becomes lawful for him by virtue of two ownerships: by virtue of the marriage and by virtue of the purchase."