What is the ruling on the prayer and fasting of one who saw pure red blood after the fifteenth day of her menstrual period, which she considered to be istihada (post-menstrual bleeding)?

If the blood exceeds 15 days, refer to your previous habit (if any), then perform ghusl and consider yourself in a state of istihada (non-menstrual vaginal bleeding). If you do not have a habit but can distinguish between menstrual blood and other blood, then consider the duration you distinguished as menstruation (provided it is not less than one day and one night, nor more than 15 days), and anything else as istihada. However, if you have neither a habit nor a distinguishing ability, then consider the duration of menstruation to be six or seven days, then perform ghusl and consider yourself in a state of istihada. The prayer and fasting of a woman in istihada are valid, and you must make up any prayers you missed during the state of istihada.