It is narrated from Sayyidah Asma' (may Allah be pleased with her) that a woman came to the Prophet (peace and blessings be upon him) and said: If menstrual blood gets on the clothes of one of us, what should she do? He (peace and blessings be upon him) said: "She should scrape it off, then clean it with water, then sprinkle water over it, and then pray in it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4083