It is narrated from Sayyidah Aishah (may Allah be pleased with her) that Fatimah bint Abi Hubaysh (may Allah be pleased with her) said: O Messenger of Allah! I suffer from istihadah (prolonged bleeding) and do not become pure; shall I then leave the prayer now? He (peace and blessings be upon him) said: "That is not menstruation; it is only a vein. When the menstruation comes, leave the prayer, and when it ends, or he said: when it passes, wash off the blood and pray."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21267