It is narrated from Sayyidah Aishah (may Allah be pleased with her) that Fatimah bint Abi Hubaysh (may Allah be pleased with her) came to the Prophet (peace and blessings be upon him) and said: O Messenger of Allah! I have prolonged bleeding (istihadah); I do not become pure. So shall I abandon the prayer? The Messenger of Allah (peace and blessings be upon him) said: "That is a vein; it is not menstruation. When menstruation comes, abandon the prayer, and when it has gone, wash the blood off yourself, then pray."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1566