Musannaf Ibn Abi Shayba 19:266

Abu Bakr narrated to us, he said: Muhammad ibn Bakr narrated to us, from Ibn Jurayj, he said: Ibn Khuthaym informed me, from Mujahid and Sa'id ibn Jubayr, that they both heard Ibn Abbas saying regarding the man who is found or caught in the act of sodomy: "He is to be stoned."