Musannaf Ibn Abi Shayba 19:795

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Hasan ibn Salih, from al-Sa’di, from ‘Adi ibn Thabit, from al-Bara’, he said: I met my maternal uncle and he had the banner with him. I said to him: "Where are you going?" He said: "The Prophet, may Allah bless him and grant him peace, sent me to a man who married his father’s wife, to kill him or strike his neck."