If a husband conditionally divorces his wife upon her menstruation ('If you menstruate, you are divorced'), and she claims menstruation, what is the ruling if he affirms or denies her claim?
Chapter on Explicit Divorce and Others
Al-Mughni
Book of Divorce
Primary text
If the husband affirms her claim, the wife is divorced. If he denies it, there are two narrations. The primary, established view is that her statement is accepted because she is entrusted regarding herself, supported by the Quranic verse forbidding the concealment of what God has created in the wombs (which includes menstruation and pregnancy). The secondary view is that her statement is not accepted, and women must examine her by inserting cotton during the claimed time to verify the presence of blood.
Supporting text
If the primary view is followed (accepting her word), there are two opinions on whether her oath is required. If the husband said, 'If you menstruate, you are divorced, and this woman [the co-wife] is with you,' and she claims menstruation and he affirms, the first wife is divorced immediately, but the second is not until she knows, as the wife is entrusted regarding herself only, not the other's status. If the husband denies the first wife's claim, she is divorced based on his admission.