It is narrated from Sayyidah Aishah (may Allah be pleased with her) that Umm Habibah bint Jahsh (may Allah be pleased with her) asked the Prophet (peace and blessings be upon him) for a ruling, saying: I have prolonged bleeding (istihadah). He (peace and blessings be upon him) said: "That is a vein, so take a ritual bath, then pray." She used to take a ritual bath for every prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1572