Musannaf Ibn Abi Shayba 19:782

Abu Bakr narrated to us, he said: Uthman ibn Uthman al-Qurashi narrated to us, from Uthman al-Laythi, who said: Al-Qasim ibn Muhammad used to say regarding a man who divorced his wife, then said to her, "You committed adultery while you were my wife": He must perform li'an (imprecation).