Sahih Muslim Book 003, Hadith Number 0584.

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.

'Aisha, the wife of the Apostle (may peace he upon him), reported: The Messenger of Allah (may peace be upon him) put out from the mosque his head for me as he was in I'tikaf, and I washed it in the state that I was menstruating.