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." (AR)
English reference (AR): Vol. 1, Book 1, Hadith 294 (AR)
Arabic reference (AR): Book 1, Hadith 295 (AR)