It was narrated that Asma' bint Abi Bakr said:
"The Messenger of Allah was asked about menstrual blood that gets on clothing. He said: 'Rub it off, wash it and perform prayer in (the garment).'" (ID)
English reference (ID): Vol. 1, Book 1, Hadith 629 (ID)
Arabic reference (ID): Book 1, Hadith 672 (ID)