Maliks Muwatta Book 28, Hadith Number 54.

Section : Marriage in General.

Yahya related to me from Malik from Rabia ibn Abi Abd ar-Rahman that al-Qasim ibn Muhammad and Urwa ibn az-Zubayr said that a man who had four wives and then divorced one of them irrevocably, could marry straightaway if he wished, and he did not have to wait for the completion of her idda.