Purity
Malik :: Book 2 : Hadith 2.29.105
Yahya related to me from Malik from Hisham ibn Urwa from his father from Fatima bint al-Mundhir ibn az-Zubayr that Asma bint Abu Bakr as-Siddiq said, "A woman questioned the Messenger of Allah, may Allah bless him and grant him peace, saying, 'If menstrual blood gets onto our clothes how do you think we should deal with it?' The Messenger of Allah, may Allah bless him and grant him peace, said, 'If menstrual blood gets onto your clothes you should wash them, and sprinkle them with water before you pray in them.' "