Shama-il Tirmidhi Chapter 004, Hadith Number 001 (031).

Hazrat Aisha (Radiallahu anha) says, "I used to comb the hair of Sayyidina Rasulullah (Sallallahu alaihe wasallam), even when I was in the state of menstruation."

Commentary.
The Ulama prove from this Hadith that it permissible for a woman in her periods to look after and serve her husband. Because of the menstruation the whole body of a woman does not become najis (naapak-unclean). It is forbidden to have intercourse with her during her menstruation.