Chapter on Menstruation
The youngest age at which menstrual blood is legally recognized is nine years. The minimum length of a period is one complete day and night, while the maximum is fifteen days with their nights. The shortest interval of purity between two periods is fifteen days, and there is no upper limit to that interval.

Everything prohibited by the state of janābah is likewise prohibited to a menstruating woman, along with crossing a mosque if she fears soiling it, fasting—which must later be made up, unlike the prayer—and sexual enjoyment of the area between her navel and knees. Another view confines the prohibition to intercourse alone. Once the bleeding stops, nothing becomes permissible before the ritual bath except fasting and the issuing of a divorce.

Irregular bleeding (istihāḍah) is an ongoing minor impurity, like chronic incontinence; it therefore does not bar a woman from fasting or prayer. In such a case she should wash her private part, secure it with a bandage, perform wuḍūʾ when the time of prayer begins, and pray without delay. If she postpones the prayer for a valid benefit—such as covering herself or waiting for the congregation—there is no harm; otherwise, the delay is harmful according to the sound opinion. A fresh ablution is required for every obligatory prayer, and—according to the sounder view—the bandage must likewise be renewed each time.

If the bleeding ceases after she has performed wuḍūʾ and she is not accustomed to such pauses and returns, or she is accustomed but the pause is long enough to accommodate ablution and the prayer itself, she must perform a new ablution.

Section
If a woman of menstrual age sees blood for at least the minimum period and it does not exceed the maximum, then all of it counts as menstruation, and—on the sounder view—so do yellowish or brownish discharges. Should the bleeding go beyond the maximum, then:
• If she is a beginner who can distinguish between a strong and a weak flow, the weak flow is treated as istihāḍah and the strong as menstruation, provided that the strong flow is not shorter than the minimum, does not exceed the maximum, and the weak flow does not reduce the purity interval below its minimum.
• If she is a beginner who cannot make such a distinction—either because the blood appears in only one form or because a condition for distinguishing is lacking—the more apparent view is that her menstruation is fixed at one day and one night.