Musnad Ahmad 1153:1663

Waki’ narrated to us, he said: Al-A’mash narrated to us, from Habib ibn Abi Thabit, from ‘Urwah, from ‘Aishah: Fatimah bint Abi Hubaysh came to the Prophet, may Allah bless him and grant him peace, and said: "O Messenger of Allah, I am a woman who experiences *istihadah* (prolonged non-menstrual bleeding) and I do not become pure. Should I abandon the prayer?" He said: "No. Avoid the prayer during the days of your menstruation, then perform *ghusl* (full ablution) and perform *wudu* (ablution) for every prayer, then pray, even if the blood drips onto the mat." And Waki’ said: "Sit for the days of your *aqra’* (menstrual cycles), then perform *ghusl*."