Does intercourse in the proper site while the wife is menstruating, post-partum bleeding, in the state of Ihram (pilgrimage restriction), or while fasting, remove the impediment of 'Innah'?
Chapter on the Term for the Impotent and the Castrated who is not amputated
Al-Mughni
Book of Marriage
Primary text
If a man penetrates his wife vaginally while she is menstruating, in post-partum bleeding (nifas), while he is in the state of Ihram, or while he is fasting, the impediment of 'Innah' is removed. This is because intercourse occurred in the proper location, which lifts the impediment, similar to when intercourse causes the wife harm due to illness. The impediment of 'Innah' is the inability to perform intercourse, and this inability cannot remain when intercourse is present, as inability is the opposite of capability.
Supporting text
The view of the Qadi suggests that the consistent position (Qiyas) of the Madhhab is that 'Innah' is not removed because Ahmad explicitly stated that such an act does not establish marital chastity ('Ihsan') or permissibility for the first husband, comparing it to intercourse in the anus as it is a forbidden intercourse. However, this reasoning is rejected because those other rulings (Ihsan, Ihlal) may be nullified due to a barrier or failure of a prerequisite, whereas 'Innah' itself is a tangible reality whose continued existence is inconceivable when penetration occurs.