Urwah bin al-Zubayr and al-Qasim bin Muhammad (may Allah have mercy on them both) both said, concerning a man who has four wives and divorces one of them irrevocably, that he may marry whenever he wishes and need not wait for her waiting period to pass.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13850