Is it obligatory to make up the prayers on the sixth and eighth days of the menstrual cycle if the bleeding stops on those days, given that the cycle was previously 7 days and sometimes 8 days?

If the bleeding stops completely on the fourth and fifth day, with complete dryness or the white discharge (al-qassah al-bayḍā’), then these two days are days of purity (ṭuhr). The woman should perform ghusl (ritual bath), and she is considered to have the ruling of those who are pure. If she then sees blood on the sixth day, she is menstruating (ḥā’iḍ) and must refrain from prayer and fasting until the bleeding stops, as long as the days of menstruation and purity do not exceed fifteen days.