Sayyidah Aishah (may Allah be pleased with her) said that Fatimah bint Abi Hubaysh al-Asadiyyah (may Allah be pleased with her) came to the Messenger of Allah (peace and blessings be upon him) to ask him for a ruling. She suffered from istihadah (prolonged bleeding), and she said: By Allah, O Messenger of Allah, I do not become pure; shall I leave the prayer because of this? The Messenger of Allah (peace and blessings be upon him) said: "That is only a vein, not menstruation. When the menstruation comes, leave the prayer, and when it ends, wash off the blood and pray."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21266