What is the ruling if menstrual blood returns after a period of proven purity?
Chapter on Menstruation
Al-Mughni
Book of Purification
Primary text
If the blood returns after a proven period of purity, the ruling depends on whether it returns during the customary time (ada) or after it. If it returns during the customary time, there are two narrations. The first is that it is part of her menstruation because it coincides with the time of her habit, similar to if the bleeding had not stopped. This is the view of Al-Thawri, the Ashab al-Ra'y, and Al-Shafi'i. The second view is that it is not menstruation, which aligns with the apparent position of Al-Kharqi and Ibn Abi Musa, because it returned after a valid period of purity, resembling a return after the established habit period.
Supporting text
If the returning blood after the habit period exceeds the maximum duration of menstruation and is not followed by the minimum period of purity, then the entire flow is considered istihada because it cannot be entirely classified as menstruation. If it returns during the habit period and exceeds the habit but not the maximum duration of menstruation, there are three views on how to classify the portion exceeding the habit: either all of it is menstruation, or only the portion matching the habit is menstruation while the excess is istihada, or all of it is istihada due to admixture with non-menstrual flow.