Imam Malik's Muwatta, Chapter: Divorce

Yahya related to me from Malik from Nafi that Abdullah ibn Umar said that a female slave who was the wife of a slave and then was set free, had the right of choice as long as he did not have intercourse with her. Malik said, "If her husband has intercourse with her and she claims that she did not know, she still has the right of choice. If she is suspect and one does not believe her claim of ignorance, then she has no choice after he has had intercourse with her."