What is the ruling on prayer and fasting if the menstrual cycle lasts 12-13 days, then the bleeding stops for a week, then a small amount of intermittent blood appears for days, and after 17 days the second menstrual cycle begins? And is fasting and prayer obligatory in this case?

If a woman sees blood after it has ceased for thirteen days or more, it is a new menstruation (hayd). She must refrain from fasting and prayer, even if its duration is long, as long as it does not exceed fifteen days. However, if the blood appears less than thirteen days after the cessation of menstruation, it is irregular bleeding (istihada).

If istihada is confirmed, the woman acts according to her known custom. What coincides with her custom is considered hayd, and anything beyond that is istihada. She performs ghusl (ritual bath) after her customary days, then prays and fasts, and performs wudu (ablution) for each prayer after its time has begun, taking precautions. If she does not have a custom, she acts based on discerning the good (distinguishing between hayd and istihada based on color, consistency, etc.), otherwise she considers herself to be in hayd for six or seven days of the month through investigation, then she performs ghusl and does what a woman in istihada does.