It was narrated from Asma' bint Abi Bakr taht a woman asked the Messenger of Allah (ﷺ) about menstrual blood that gets on clothes. He said:
"Scratch it, then rub it with water, then sprinkle water over it, and pray in it." (RU)
English reference (RU): Vol. 1, Book 1, Hadith 294 (RU)
Arabic reference (RU): Book 1, Hadith 295 (RU)