Maliks Muwatta Book 029, Hadith Number 006.

Section : The 'Irrevocable' Divorce.

Yahya related to me from Malik that he had heard that Ali ibn Abi Talib used to say that if a man said to his wife, "You are haram for me," it counted as three pronouncements of divorce.

Malik said, "That is the best of what I have heard on the subject."