What is the ruling regarding the fast of a wife whose menstruation has ceased due to an IUD, then she experiences bleeding, and doctors disagree as to whether it is menstruation or istihada (non-menstrual vaginal bleeding)?

The basic rule regarding blood discharged by a woman is that it is menstrual blood unless it exceeds 15 days. If a woman uses something to prevent menstruation, her cycle might become disrupted. In such cases, the characteristics of the blood should be examined to distinguish between menses and abnormal bleeding (istihada).

If a woman fasts, believing the blood to be istihada, and then it becomes clear that it was menstrual blood, she must make up the fasts, as fasting is not valid during menstruation. However, if she relied on the doctor's statement, it is hoped that this will be an excuse for her, as scholars may excuse ignorance in such matters.