Yahya related to me from Malik from Nafi from Sulayman ibnYasarfrom Umm Salama, the wife of the Prophet, may Allah bless him andgrant him peace, that a certain woman in the time of the Messenger ofAllah, may Allah bless him and grant him peace, used to bleedprofusely, so Umm Salama consulted the Messenger of Allah, may Allahbless him and grant him peace, for her, and he said, "She shouldcalculate the number of nights and days a month that she used tomenstruate before it started happening, and she should leave off fromprayerfor that much of the month. When she has completed that sheshould do ghusl, bind her private parts with a cloth, and then pray."
USC-MSA web (English) reference: Book 2, Hadith 107
Arabic reference: Book 2, Hadith 136