Musnad Abu Ya'la al-Mawsili 149:138

Ibrahim narrated to us, Hammad narrated to us, from Muhammad ibn Ishaq, from Yahya ibn 'Abbad, from 'Aisha, that she said: They differed regarding the washing of the Prophet (peace be upon him), and sleep was cast upon them, so there was not one of them but that his chin was upon his chest. Then they were called from a side of the house: "Wash him from behind his shirt." 'Aisha said: "If I had known in the beginning of my affair what I knew in the end, no one would have washed the Messenger of Allah (peace be upon him) except his wives."