From Sahih Bukhari (Hadith 327):
Narrated `Aisha:(the wife of the Prophet) Um Habiba got bleeding in between the periods for seven years. She asked Allah's Messenger (ﷺ) about it. He ordered her to take a bath (after the termination of actual periods) and added that it was (from) a blood vessel. So she used to take a bath for every prayer
Reference: Bukhari 327