What is the ruling on combining separate instances of menstrual blood separated by a period of purity (tuhur)?
Chapter on Menstruation
Al-Mughni
Book of Purification
Primary text
If a woman experiences a period of purity (tuhur) in the middle of menstruation, that purity is considered valid. If she sees blood, then purity, then blood again, and the total duration does not exceed the maximum limit of menstruation, all the blood is combined (talfeeq) to constitute a single menstrual period, and the intervening clean period is considered true purity. This applies regardless of whether the time of bleeding is longer than, equal to, or shorter than the time of purity, such as seeing two days of blood and one day of purity, or vice versa, provided the blood recurs and does not exceed the maximum duration of menses. If the total time of blood seen is less than a full day, such as half a day of blood and half a day of purity, the ruling is the same: the blood is combined to form menses, and the intervening time is purity, provided the combined blood reaches the minimum duration of menses. This ruling aligns with the position of Al-Shafi'i.
Supporting text
If the accumulated blood does not reach the minimum duration of menses, it is considered blood of corruption (damm fasad). There is an opposing view that the blood does not constitute menses unless it is preceded by an uninterrupted, valid menstrual flow. Furthermore, if the intervening purity is less than one day, there is a view that it is not considered purity at all; consequently, all the blood, including that separated by less than a day, becomes menses if the total duration meets the minimum requirement.