Al-Qa'qa' bin Hakim asked Sa'id bin al-Musayyib (may Allah have mercy on him) about the woman with prolonged bleeding (istihadah), and he said: "O my nephew! There is no one who knows this better than I do. When menstruation comes, abandon the prayer, and when it (the menstruation) has gone, take a ritual bath and pray."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1569