What is the expiation for having intercourse with one's wife anally?

Anal intercourse with one's wife is forbidden and is considered among the grave sins. The Prophet, peace and blessings be upon him, cursed the one who commits such an act. There is no expiation for this forbidden act other than sincere repentance (tawbah nasuh), which involves abstaining from the sin, regretting it, and resolving never to return to it, along with increasing good deeds. Whoever repents sincerely, Allah will accept their repentance. The wife does not become unlawful to her husband because of this act. However, she must refuse and demand the annulment of the marriage if the husband does not repent. The absence of an expiation for the act does not mean it is minor; rather, it may indicate the gravity of the sin.