Sayyiduna al-Bara' (may Allah be pleased with him) said: I met my maternal uncle and he had a banner with him, so I asked: Where are you going? He said: "The Messenger of Allah (peace and blessings be upon him) has sent me to a man who married his father's wife after him, so that I strike his neck and kill him."
Hadith Referenceالمعجم الكبير للطبراني / باب الهاء / 18729