Musannaf Ibn Abi Shayba 9:908

Ahmad ibn Ishaq narrated to us, from Wahb, from Suhayl ibn Abi Salih, from al-Harith ibn Makhlad, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Allah does not look at a man who has intercourse with his wife in her anus."