Musnad Ahmad 27:30

Isma'il narrated to us, Ayyub narrated to us, from Sa'id ibn Jubayr, who said: I said to Ibn Umar: A man accused his wife of adultery. He said: The Messenger of Allah (may Allah bless him and grant him peace) separated the two brothers of Banu al-'Ajlan, and he said: "Allah knows that one of you is a liar, so is there any repentant one among you?" They both refused, so he repeated it to them three times. They both refused, so he separated them.