Is it obligatory for the questioner to marry the girl whom he had an anal sexual relationship with—at the age of 14, with her mother's knowledge—as an expiation for his sin, or is there another expiation?

"Whoever has anal intercourse with a woman has committed a grave sin and is cursed. If he does this with a woman unlawful to him, his sin is even greater.

However, Allah has legislated repentance and encouraged it, for He loves those who repent, and He transforms the bad deeds of the penitent into good deeds. He forgives all sins for whoever repents and turns to Him, even if their sins reach the clouds of the sky.

Therefore, the first thing you should do to atone for your sin is to offer sincere repentance to Allah.

If this girl repents from the sin, then there is no harm in marrying her; in fact, it is better, because good deeds obliterate bad deeds. The more the good deeds are of the same kind as the bad deeds but antithetical to them, the more effective they are in expiation.

As for the mother who betrayed the trust and assisted in the indecency, her crime is grave, and she must hasten to repent before Allah's punishment befalls her. For Allah has forbidden Paradise to whoever deceives their flock, and to the cuckold (dayyuth) who condones evil among his family.

Whoever repents, Allah accepts his repentance. Whoever persists in sin will only harm himself."