What are the evidences that the majority of scholars relied upon in determining the maximum duration of menstruation to be 13-15 days, and what is the maximum duration of purity (Tuhr) according to most scholars, with a mention of the evidences from the Qur’an and Sunnah?

Scholars have differed in determining the maximum duration of menstruation. The majority are of the view that it is fifteen days, and anything beyond that is considered irregular bleeding (istihāḍah). They based their reasoning on custom and common practice, and that the period of purity (ṭuhr) cannot be less than the duration of menstruation. As for determining the minimum period of purity between two menstruations, there is no minimum limit for it, nor is there a maximum limit for the period of purity between two menstruations, by the consensus of scholars. This is because it is observed and witnessed, and among women, some remain pure for a month or more, while others do not menstruate at all.