There is disagreement concerning a woman whose customary menstrual periods vary in length. The well-known opinion is that she observes additional precautionary days after her customary days. Ibn Habīb said that she observes them after her shortest customary period. Ibn Lubāba held that she performs the ritual bath at the end of her shortest customary period, without observing any additional precautionary days, and is then considered to have irregular bleeding. This is a manifest error, contradicted by the Quran and invalidated by reasoned consideration.

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Menstrual bleeding may occur on consecutive days or intermittently. As we have explained, the womb may discharge the blood accumulated within it during the period of purity in one continuous flow, or it may discharge it little by little. Continuous bleeding has already been discussed. In the case of intermittent bleeding, the ruling is that she adds together the days of bleeding and disregards the intervening days of purity. Once the bleeding days total her customary days together with the additional precautionary days, or fifteen days, according to the disagreement mentioned above, she is considered to have irregular bleeding. She then disregards any blood she sees until the minimum period of purity has elapsed, counting from the day on which she was deemed to have irregular bleeding.

Whenever the bleeding stops, she performs the ritual bath, prays, and fasts. Any day on which she sees blood, even during only part of it, counts as a day of bleeding rather than a day of purity, even if she sees blood for only an hour or sees only a spot.

According to Mālik and his companions, the days of purity are not added together. The exception is Muhammad ibn Maslama, who held that she keeps a cumulative count of both the days of bleeding and the days of purity. She thus continues indefinitely to be considered menstruating on the days of bleeding and pure on the days of purity, provided that the bleeding days equal or are fewer than the days of purity—for example, if she bleeds for one day and is pure for one day, or bleeds for two days and is pure for two days. If, however, she bleeds for two days and is pure for one day, she adds together the days of bleeding and disregards the days of purity. She is considered to have irregular bleeding once the bleeding days total her customary menstrual days, since, as we have already mentioned, he does not prescribe additional precautionary days.

The same ruling applies to postpartum bleeding when it is intermittent rather than continuous: she adds together the days of bleeding and disregards the days of purity until she reaches the maximum duration of postpartum bleeding, concerning whose limit there is disagreement. If the bleeding exceeds that maximum, she is then considered to have irregular bleeding. For postpartum bleeding has no additional precautionary days as menstruation does: menstruation follows an established pattern and has customary days, and postpartum bleeding does not have the same duration. Consider whether, according to Ibn Maslama’s position, the days of purity may also be added together in the case of postpartum bleeding. I do not consider this implausible.