Musnad Ahmad 944:9

Sufyan ibn 'Uyaynah narrated to us, from Yazid ibn 'Abdullah ibn al-Had, from 'Umarah ibn Khuzaymah, from his father, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Allah is not ashamed of the truth. Do not approach women in their anuses."