Sahih Muslim
The Book of Menstruation (Kitab Al-Haid)
Book Number: 003 / Hadith Number: 582
It is reported from 'A'isha that she observed: When the Messenger of Allah (may peace be upon him) was in I'tikaf, he inclined his head towards me and I combedhis hair, and he did not enter the house but for the natural calls (for relieving himself).