Musnad Ahmad 1153:2317

Ya'qub narrated to us, he said: Ibn Akhi Ibn Shihab informed us, from his uncle, who said: Urwah ibn al-Zubayr informed me, from Aisha, that she said: "She used to comb the hair of the Messenger of Allah, may Allah bless him and grant him peace, while she was menstruating, and the Messenger of Allah, may Allah bless him and grant him peace, was in I'tikaf in the mosque. He would lean toward the threshold of Aisha's room, and she would wash his head while she was in her room."