Sayyidah Aishah (may Allah be pleased with her) said that Fatimah bint Hubaysh (may Allah be pleased with her) came to the Prophet (peace and blessings be upon him) and said: I suffer from istihadah (prolonged bleeding); shall I leave the prayer? He (peace and blessings be upon him) said: "When the menstruation comes, leave the prayer for its duration, then wash off the blood and pray."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21259