Sunan Abu Dawud
291
Sahih+1

Aishah said:Umm Habibah had a prolonged flow of blood for seven years. The Messenger of Allah (ﷺ) commanded her to take bath; so she used to take bath for every prayer

SahihAl-Albani
Sahih Bukhari (327) Sahih Muslim (334)Zubair Ali Zai