Is ghusl and prayer obligatory when menstruation ceases on the fifth day, then stopped upon the return of blood, or are ghusl and prayer not obligatory during this fluctuating period?

A woman recognizes purity from menstruation by one of two signs: dryness or the white discharge. She must perform ghusl (ritual bath) and pray as soon as she sees purity by either of these signs, and she then has the rulings of pure women. If blood returns during a time when it can be considered menstruation, she reverts to being a menstruating woman. The purity that intervenes within a menstrual period is valid purity. If the blood stops after its return, she performs ghusl again.