Musnad Ahmad 1153:1987

Yazid narrated to us, he said: Muhammad—meaning Ibn Ishaq—informed us, from al-Zuhri, from Urwah, from Aisha, that Zaynab bint Jahsh experienced *istihada* (prolonged non-menstrual bleeding) during the time of the Messenger of Allah, peace and blessings of Allah be upon him. The Messenger of Allah, peace and blessings of Allah be upon him, commanded her to perform ghusl (ritual bath) for every prayer. She would enter a large basin filled with water and submerge herself in it, then emerge from it, while the blood was still flowing over her, and she would come out and pray.