Maliks Muwatta Book 28, Hadith Number 40.
Yahya related to me from Malik from Ibn Shihab, and he had heard from al-Qasim ibn Muhammad that they said, “When a free man marries a slave-girl and consummates the marriage, she makes him muhsan.”
Malik said, “All (of the people of knowledge) I have seen said that a slave-girl makes a free man muhsan when he marries her and consummates the marriage.”
Malik said, “A slave makes a free woman muhsana when he consummates a marriage with her and a free woman only makes a slave muhsan when he is freed and he is her husband and has had sexual relations with her after he has been set free. If he parts from her before he is free, he is not a muhsan unless he marries her after having been set free and he consummates the marriage.”
Malik said, “When a slave-girl is married to a free man and then he separates from her before she is set free, his marriage to her does not make her muhsana. She is not muhsana until she has married after she has been set free and she has had intercourse with her husband. That gives her ihsan. If she is the wife of a freeman and then she is set free while she is his wife before he separates from her, the man makes her muhsana if he has intercourse with her after she has been set free.”
Malik said, “The christian and jewish free women and the muslim slave-girl all make a muslim free man muhsan when he marries one of them and has intercourse with her.”