Sunnan Abu Dawud Collection: ::Book Number 38:: Hadith # 4442
Narrated Al-Bara' ibn Azib: I met my uncle who was carrying a standard. I asked him: Where are you going? He said: The Apostle of Allah (peace_be_upon_him) has sent me to a man who has married his father's wife. He has ordered me to cut off his head and take his property.