Answer
It is permissible for the husband to enter his wife from the front or rear,
but not in the anus. Anal sex is Haraam.
Hadhrat ibn Abbaas (Radhiallaahu Anhu) narrates that the following Aayat was
revealed to Nabi (Sallallaahu Alayhi Wasallam), ‘Your wives are a tilth
(farm) unto you, so go to your tilth (have sexual relations with your wives
in any manner as long as it is in the vagina and not in the anus) when or
how you will .’ (Surah Baqaraha Aayat223). Go from the front or from the
back, but stay away from the anus and the period of menses.’ (Mishkaat
pg.276)
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai