How is menstruation counted for a woman whose bleeding exceeds the maximum period of menses, who cannot distinguish blood colours, and who forgot last month's dates but remembers the number of days?

Summary

This woman falls under the sixth category of mustahadah, the mutahayyirah ghair mumayyizah who remembers the number of her menstrual days but not when they began. Days certain to be menstruation take the ruling of menstruation, while days certain to be purity take the ruling of istihadah. Days that may be either menstruation or purity require caution in worship, and ablution suffices for each obligatory prayer. Days that may be menstruation, purity or a cessation of blood also require caution, together with a full obligatory bath for each obligatory prayer.

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