Musnad Ahmad 1167:21

Yahya ibn Sa'id narrated to us, from Hisham, who said: Fatimah narrated to me, from Asma'; and Abu Mu'awiyah said: Hisham narrated to us, from Fatimah, from Asma', that a woman came to the Messenger of Allah, may Allah bless him and grant him peace, and said: "One of us gets the blood of menstruation on her garment?" He said: "She shall scrape it, then rub it with water, then rinse it, then pray in it."