Maliks Muwatta Book 28, Hadith Number 29.

Section : Marrying Slaves when already Married to Free Women.

Yahya related to me from Malik from Yahya ibn Said that Said ibn al-Musayyab said, “The slave girl is not married when there is a free woman who is a wife unless the free woman wishes it. If the free woman complies, she has two-thirds of the division of time.”

Malik said, “A free man must not marry a slave-girl when he can afford to marry a free-woman, and he should not marry a slave-girl when he cannot afford a free woman unless he fears fornication. That is because Allah, may he be Blessed and Exalted, says in His Book, ‘If you are not affluent enough to marry believing women, who are muhsanat, take slave-girls who are believing women that your right hands own.’ (Sura 4 ayat 24) He says, ‘That is for those of you who fear al-anat.'”

Malik said, “Al-anat is fornication.”