Musannaf Ibn Abi Shayba 1:1346

Ibn Numayr and Abu Usamah narrated to us, from Ubaydullah ibn Umar, from Nafi, from Sulayman ibn Yasar, from Umm Salamah, who said: A woman asked the Prophet, peace and blessings of Allah be upon him, and said: "I experience *istihada* (prolonged non-menstrual bleeding) and do not become pure, so should I abandon the prayer?" He said: "No, but abandon the number of days and nights that you used to menstruate, and the duration of them, then perform *ghusl* (ritual bath), bind yourself with a cloth, and pray." Except that Ibn Numayr said: Umm Salamah asked the Prophet, peace and blessings of Allah be upon him, and a woman said: "I am shedding blood." He said: "She should wait for the number of days and nights that she used to menstruate, or the duration of them from the month." Then he mentioned the like of Abu Usamah’s hadith.