It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her) that in the time of the Prophet (peace and blessings be upon him) a woman kept bleeding. Sayyidah Umm Salamah (may Allah be pleased with her) asked about her, and the Messenger of Allah (peace and blessings be upon him) said: "Let her look at the number of her days and nights in the month during which she used to menstruate before, and abandon the prayer on that account. When that (period) has passed, let her take a ritual bath, bind herself with a cloth and pray."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1582