What is it like to have intercourse in the rear private part of the wife?
According to the consensus of the jurists, sexual intercourse in the rear private part of the wife is haram. He should repent and renew his faith and marry۔
من أتی حائضا أو امرأة في دبرها أو کاهنا فقد کفر بما أنزل علی محمد ﷺ
Whoever has sexual intercourse with a menstruating or pregnant woman or comes to a priest has disbelieved in what was revealed to the Prophet ﷺ.