Musnad Ahmad 1153:525

Abu al-Mughirah narrated to us, he said: al-Awza’i narrated to us, he said: al-Zuhri narrated to me, from ‘Urwah, from ‘Amrah bint ‘Abd al-Rahman ibn Sa’d ibn Zurarah, that ‘Aishah, the wife of the Prophet, may Allah bless him and grant him peace, said: Umm Habibah bint Jahsh, while she was under [the marriage of] ‘Abd al-Rahman ibn ‘Awf, experienced *istihada* (prolonged non-menstrual bleeding) for seven years. She complained of that to the Messenger of Allah, may Allah bless him and grant him peace. The Prophet, may Allah bless him and grant him peace, said: "Indeed, this is not the menstruation; it is only a vein. So when the menstruation approaches, leave the prayer, and when it departs, perform ghusl (ritual bath), then pray." ‘Aishah said: "She used to perform ghusl for every prayer, then pray. And she used to sit in a washbasin for her sister, Zaynab bint Jahsh, until the redness of the blood would rise above the water."