Musnad Ahmad 944:25

Ya'qub narrated to us, he said: I heard my father narrating from Yazid ibn 'Abdullah ibn Usamah ibn al-Had, that 'Ubaydullah ibn al-Husayn al-Walibi narrated to him, that Harmi ibn 'Abdullah al-Waqifi narrated to him, that Khuzaymah ibn Thabit al-Khatmi narrated to him, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Allah is not ashamed of the truth. Allah is not ashamed of the truth." (He said it three times). "Do not approach women in their posteriors."