Imam Malik's Muwatta, Chapter: Marriage

Yahya related to me from Malik that he had heard that Said ibn al-Musayyab and Sulayman ibn Yasar were asked whether, when a man married a slave of his to a slave-girl and the slave divorced her irrevocably, and then her master gave her to the slave, she was then halal for the slave by the possession of the right hand. They said, "No. She is not halal until she has married another husband."