Musnad Abu Ya'la al-Mawsili 106:13

Isma'il ibn Ibrahim narrated to us, Hushaym narrated to us, Ash'ath informed us, from 'Adi ibn Thabit, from al-Bara' ibn 'Azib, who said: The Messenger of Allah (may Allah bless him and grant him peace) sent my maternal uncle to a man who had married the wife of his father, and he ordered him to strike his neck.