Is it necessary to make up for the fasting days during which blood descended after your menstrual period, and you were unable to distinguish between menstrual blood (hayd) and irregular bleeding (istihada), knowing that you did not abandon fasting or prayer during that period?

This issue is based on a difference of opinion among scholars regarding the minimum period of purity (Tuhr) between two menstrual cycles.

- The opinion of the majority: The minimum period of purity is fifteen days. Accordingly, the blood you saw before the completion of 15 days from the previous menstruation is considered irregular bleeding (Istihada). You must perform ablution (Wudu') for each prayer after its time has begun, and you should revert to your previous habit, or differentiate (between menstrual and non-menstrual blood), or follow the general habit of women.

- The opinion of the Hanbalis: The minimum period of purity is thirteen days. Accordingly, the blood you saw is menstrual blood, and you must make up for the days you fasted during it. This opinion is the more cautious one to avoid dispute.