Is anal intercourse with one's wife considered disbelief (kufr)? Does it make the wife unlawful (haram) thereafter? And is a specific punishment (hadd) or expiation (kaffara) required to purify oneself from this sin?

Anal intercourse is forbidden and a grave abomination that incurs a curse. One who commits it, without deeming it permissible, is not an infidel, but rather guilty of ingratitude for blessings (kufr ni'mah). This act does not render the wife unlawful, nor does it entail a prescribed punishment (hadd) or expiation (kaffarah). What is obligatory is repentance to Allah by abandoning the sin, regretting it, and resolving never to return to it, along with increasing righteous deeds. No matter how great the sin, Allah accepts sincere repentance and transforms evil deeds into good ones, for repentance erases what came before it.