Musannaf Ibn Abi Shayba 18:1155

Abu Bakr narrated to us, he said: Abda narrated to us, from Yahya bin Sa’id, from Sa’id bin al-Musayyib: That a man from the people of Syria, who was called Ibn Khaybari, found a man with his wife, so he killed him, or he killed them both. The matter was raised to Mu’awiyah, and the judgment regarding that became difficult for him. So he wrote to Abu Musa, "Ask Ali about that." Abu Musa asked Ali, and he (Ali) said, "This is something that does not happen in our land. I adjure you to tell me." So he informed him. Ali said, "I am Abu Hasan: if he does not bring four witnesses, then they should hand him over to them (the family of the victim) for his retaliation."