It is narrated from Sayyidah Asma bint Abi Bakr al-Siddiq (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) was asked about a garment stained by menstrual blood, and he (peace and blessings be upon him) said: "(The woman) should scrape it, then rub it with water, then sprinkle it with water and pray in it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 35