Sayyiduna al-Bara' (may Allah be pleased with him) said: My uncle met me, and he had tied a banner. I asked: "Where are you going?" He said: "The Prophet (peace and blessings be upon him) has sent me to a man who has married his father's wife, to strike his neck and take his property."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المرتد / 16893