Sahih Bukhari Volume 1, Book 6, Hadith Number 304

Narated By Asma’ bint Abi Bakr : A woman asked Allah’s Apostle, “O Allah’s Apostle! What should we do, if the blood of menses falls on our clothes?” Allah’s Apostle replied, “If the blood of menses falls on the garment of anyone of you, she must take hold of the blood spot, rub it, and wash it with water and then pray in (with it).”