Maliks Muwatta Book 29, Hadith Number 2.

Section : The ‘Irrevocable’ Divorce.

Yahya related to me from Malik that he had heard that a man came to Abdullah ibn Masud and said, “I have divorced my wife by saying I divorce you eight times.” Ibn Masud said to him, “What have people told you?” He replied, “I have been told that I have to part absolutely from her.” Ibn Masud said, “They have spoken the truth. A person who divorces as Allah has commanded, Allah makes it clear for him, and a person who obscures himself in error, we make stay by his error. So do not confuse yourselves and pull us into your confusion. It is as they have said.”