It is narrated from Sayyidah Aishah (may Allah be pleased with her) that Fatimah bint Abi Hubaysh (may Allah be pleased with her) used to have prolonged bleeding (istihadah), so she asked the Messenger of Allah (peace and blessings be upon him) about that, and he (peace and blessings be upon him) said: "That is from a vein; it is not menstruation. When menstruation comes, abandon the prayer, and when it has gone, take a ritual bath and pray."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1555