Maliks Muwatta Book 29, Hadith Number 28.
Section : The Option (of Slave-Girls Married to Slaves when Freed).
Yahya related to me from Malik that he had heard that Said ibn al-Musayyab said that if a man married a woman, and he was insane or had a physical defect, she had the right of choice. If she wished she could stay, and if she wished she could separate from him.