Musnad Ahmad 435:52

Abdullah ibn Ahmad said: I found this hadith in my father’s book in his own handwriting: Bakr ibn Yazid narrated to us—and I think I heard it from him during a study session, but I did not write it down, and Bakr used to stay in Medina; I think it was during the *Mihna* (Inquisition) that he had crossed out this hadith in his book—he said: Bakr ibn Yazid narrated to us, he said: Abu Bakr, meaning Ibn Abi Maryam, informed us, from Atiyyah ibn Qays al-Kilabi, that Mu’awiyah ibn Abi Sufyan said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The two eyes are the tie of the anus; so when the two eyes sleep, the tie is released."