and its thickness, it is not menstruation. Whatever lasts less than a day and a night is not menstruation. This is the established position of the school.

They argued that it is not customary for menstruation to last less than a day and a night; therefore, since this does not ordinarily occur, its minimum should be one day and one night.

But this is not evidence, for some women do not menstruate at all, while others menstruate for a few hours and then become pure. The sound view, therefore, is that there is no minimum limit.

His statement, “Its maximum is fifteen days,” means the maximum duration of menstruation. This is the established position of the school.

They argued on the basis of customary practice: ordinarily, a woman’s menstruation does not exceed fifteen days. Furthermore, anything beyond this period would occupy most of the month, whereas the period of purity cannot be shorter than the period of menstruation.

Thus, if it were sixteen days, the period of purity would be fourteen days. Yet the duration of bleeding cannot exceed that of purity. The scholars hold that when bleeding continues uninterruptedly, a woman is considered to have irregular bleeding. Therefore, the greater part of the month is given the ruling of the whole, and whatever exceeds fifteen days is deemed irregular bleeding. Hence, any woman whose bleeding exceeds fifteen days is considered to have irregular bleeding.

If a woman asks about bleeding that lasted for twenty hours—whether she must make up the prayers she omitted during that period—the answer is that she must make them up, because this was not menstruation; she had in fact refrained from prayer during a period of purity.