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