Musnad Ahmad 1153:1966

Yazid narrated to us, he said: Sufyan informed us, from al-Zuhri, from Urwah, from Aisha, she said: The Messenger of Allah (peace and blessings of Allah be upon him) used to be in I'tikaf, and he would not enter the house except for human necessity. She said: So I would wash his head, while there was between me and him the threshold of the door.