Musannaf Ibn Abi Shayba 9:233

Narrated to us Abd al-A’la, from Sa’id, from Qatadah, from Sa’id ibn al-Musayyib, who said: He may have intercourse with her by right of possession (milk al-yamin), and if he wishes, he may manumit her and marry her, and she would be with him as one [of his wives]. And Qatadah used to adopt this [view].