What is the minimum age for a woman to begin menstruation?
General Chapter
Al-Mughni
Book of Waiting Periods ('Iddah)
Primary text
The minimum age for a woman to menstruate is nine years, because the reference for this is based on what has been observed to occur, and menstruation has been observed in those who are nine years old. If blood is seen before this age, it is not considered menses because it has not been observed to recur repeatedly. The criterion for consideration is that which recurs three times during a state of health, and this has not been met.
Supporting text
A narration attributed to Al-Shafi'i mentions seeing an elderly woman who was twenty-one, and if two pregnancies (about one and a half years) are subtracted from her age and the remainder divided between her and her daughter, each would have menstruated before the age of ten.