Musannaf Ibn Abi Shayba 19:277

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, from Sa’id, from Qatadah, from Jabir ibn Zayd, who said: "The sanctity of the anus is greater than the sanctity of such-and-such." Qatadah said: "We interpret it as stoning."