Sahih Muslim Book 2, Hadith Number 573.
Chapter : The Impurity of the blood of menses and its washing.
Asma (daughter of Abu Bakr) reported: A woman came to the Apostle of Allah (may peace be upon him) and said: What should one do if the blood of menses smears the garment of one amongst us? He (the Holy Prophet) replied: She should scrape it, then rub it with water, then pour water over it and then offer prayer in it.