What is the waiting period (Iddah) for a woman experiencing abnormal bleeding (Mustahadah) who has an established menstrual cycle based on habit or discerning feature?

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If a woman experiencing prolonged bleeding has an established menstrual cycle determined by habit or distinguishing features, her ruling is the same as a normal menstruating woman. Her waiting period concludes after three *quru'* (menstrual cycles/pure periods) have passed according to her known cycle length. Imam Ahmad stated that the Mustahadah must observe the duration of the *quru'* she previously knew. If she knows she bleeds every month but does not know the exact timing, her Iddah is three months. If she is uncertain about any part, she must wait until she is certain that the three *quru'* have concluded.