Musnad Ahmad 1153:2084

Uthman ibn Umar narrated to us, he said: Yunus informed us, from al-Zuhri, from Urwah, that Aisha said: "The Messenger of Allah, peace and blessings of Allah be upon him, would bring his head in to me while he was in the mosque, and I would comb his hair. He would not enter the house except for a need, unless he intended to perform ablution while he was in I'tikaf."