The Sign of Puberty and Permission for Nikah
Question
Can the nikah of a minor girl who is twelve or thirteen years old take place or not? And is this age the age of puberty or not?
Answer
If at this age she has begun to menstruate, then she is adult, and her nikah with her own permission is valid. If it is contracted outside the family, the permission of the guardian (wali) is also necessary. If she has not yet begun to menstruate, then she is a minor, and her nikah is valid with the permission of the wali.
Source: Fatawa Mahmudiyya
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