Sahih Muslim Book 003, Hadith Number 0586.

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.

Al-Aswad narrated it from 'Aisha that she observed: I used to wash the head of the Messenger of Allah (may peace be upon him), while I was in a state of menstruation.