How can a husband atone for anal intercourse with his wife in a moment of weakness, and for the shame that resulted between the couple?

If a husband engages in anal intercourse with his wife, they have committed a sin and an act forbidden by Islamic law. She is required to perform sincere repentance by regretting the sin, not returning to it, and abandoning it. Whoever repents with these conditions will have their repentance accepted by Allah, and He will forgive them.