Purity
Malik :: Book 2 : Hadith 2.29.104
Yahya related to me from Malik from Hisham ibn Urwa from his father that A'isha, the wife of the Prophet, may Allah bless him and grant him peace, said, "I used to comb the head of the Messenger of Allah, may Allah bless him and grant him peace, while I was menstruating."