Sahih Muslim Book 003, Hadith Number 0649.
Chapter : The desirability of using musk at the spot of blood while bathing after menstruation.
'Aisha reported: Asma (daughter of Shakal) asked the Apostle of Allah (may peace be upon him) about washing after menstruation. He said: Everyone amongst you should use water (mixed with the leaves of) the lote-tree and cleanse herself well, and then pour water on her head and rub it vigorously till it reaches the roots of the hair. Then she should pour water on it. Afterwards she should take a piece of cotton smeared with musk and cleanse herself with it. Asma' said: How should she cleanse herself with the help of that? Upon this he (the Apostle of Allah) observed: Praise be to Allah, she should cleanse herself. 'Aisha said in a subdued tone that she should apply it to the trace of blood. She (Asma) then further asked about bathing after sexual intercourse. He (the Holy Prophet) said: She should take water and cleanse herself well or complete the ablution and then (pour water) on her head and rub it till it reaches the roots of the hair (of her) head and then pour water on her. 'Aisha said: How good are the women of Ansar (helpers) that their shyness does not prevent them from learning religion.