Musnad Ahmad 1283:1

Muhammad ibn Salamah al-Harrani narrated to us, from Ibn Ishaq, from al-Zuhri, from Urwah, from Umm Habibah bint Jahsh, that she suffered from *istihadah* (prolonged non-menstrual bleeding), so she asked the Messenger of Allah, peace and blessings of Allah be upon him. He commanded her to perform *ghusl* (ritual washing) for every prayer. And she would emerge from the washbasin while the redness of the blood had overcome the water, and then she would pray.