Sahih Muslim Book 3, Hadith Number 582.

Chapter : The menstruating woman is permitted to wash the head of her husband, comb his hair, and her left-over is clean, and one is permitted to recline in her lap and recite the Qur’an.

It is reported from ‘Aisha 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 combed his hair, and he did not enter the house but for the natural calls (for relieving himself).