Is it permissible for a man to fondle his wife's anus with his fingers?

All praise is due to Allah.

It is permissible for spouses to enjoy each other's bodies, to look and touch, based on the Almighty’s saying: (They are a garment for you, and you are a garment for them). As for foreplay with the anus, it is of two types: external touching, which is not forbidden, though disliked; and inserting a finger, which is forbidden for several reasons:

1- Because it is a place of severe impurity. 2- It can lead to forbidden anal intercourse. 3- Sound human nature recoils from it. 4- It may lead to something more abominable. 5- What Allah has legislated for intimacy between spouses is sufficient and makes anything else unnecessary.

A Muslim should fear Allah and avoid forbidden things and their causes, for Allah knows the treachery of the eyes and what the hearts conceal.