Does intercourse in the anus 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
Intercourse in the anus does not remove the impediment of 'Innah' because the anus is not the proper site for intercourse, analogous to penetration below the vagina. Consequently, it does not establish the permissibility ('Ihlal') for the first husband, nor does it establish marital chastity ('Ihsan').
Supporting text
Ibn Aqil preferred the view that penetration in the anus removes 'Innah' on the grounds that it is more difficult; whoever is capable of that is more capable of the standard act.