Musnad Ahmad 27:496

Sufyan narrated to us, from Ayyub, from Sa'id ibn Jubayr, who said: I said to Ibn Umar, "A man who performs *li'an* (oath of condemnation) against his wife?" He said: The Messenger of Allah (peace and blessings of Allah be upon him) separated the two spouses of the Banu al-'Ajlan, and he said: "Indeed, one of you is a liar, so is there any repentant one among you?" [He said this] three times.