A question was put to the marja`:
Is there an expiation that is to be given for one engaging in anal sex with one’s wife?
The marja`, Imam `Abdur-Rahman ash-Shami, may Allah preserve him, stated the following:
There is no expiation for it but it is a grave sin in which a Divine Threat was made against it. The Prophet, peace and blessings of Allah be upon him, stated,
“Cursed is the one that approaches his wife to have anal sex with her.” This has been mentioned in the Musnad of Imam Ahmad ibn Hanbal, may Allah have mercy on him.
As for the one that had engaged in this behaviour, he must repent, seek Allah’s forgiveness and resolve not to do that activity again.
Taken from the website of the maraji`