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