It is narrated from Sayyidah Asma bint Abi Bakr (may Allah be pleased with her) that a woman asked the Prophet (peace and blessings be upon him) about menstrual blood getting on a garment, and he (peace and blessings be upon him) said: "Scrape it and then wash it, then sprinkle water on it and pray in it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4106