What should be done concerning the prayers the questioner missed, believing she was menstruating, when it later became clear it was istihadah?

The blood a woman sees is considered menses (hayd) unless it exceeds fifteen days. If the bleeding is intermittent, upon its cessation, she must perform ghusl (ritual bath) and pray. If the blood returns, it is again considered menses, and so on, until the total number of days reaches fifteen. If it exceeds fifteen days, the woman becomes a mustahadah (experiencing irregular bleeding).

The Shafi'is hold that if the blood exceeds the customary period, it is still menses unless it surpasses fifteen days; if it does, she is a mustahadah. The Hanbalis are of the view that if the blood exceeds the customary period, she is a mustahadah, and she performs ghusl, prays, and fasts. However, their preponderant view is that if the blood exceeds the customary period, it is still menses unless it exceeds fifteen days.

If a woman becomes a mustahadah (by the blood exceeding fifteen days), if she has a regular habit, she observes her customary period, then performs ghusl and ablution for each prayer. If she does not have a regular habit but can distinguish the blood (e.g., by color or thickness), she acts according to her distinction. If she has neither a regular habit nor the ability to distinguish, she observes the غالب عادة النساء (predominant custom of women), which is six or seven days.

It is obligatory to refrain from prayer upon seeing blood unless its duration exceeds fifteen days. Upon seeing purity, ghusl and prayer become obligatory. If the blood returns, she becomes a menstruating woman again until the total number of days exceeds fifteen days, at which point she becomes a mustahadah and must make up for the missed prayers that she did not perform, thinking that she was in menses during the period of istihadah.