Will the repentance of a man who committed adultery with a married woman be accepted after he regrets his action, and how can he expiate his sin?

Adultery with a married woman is one of the most heinous major sins and gravest transgressions. Sincere repentance is obligatory, and one must abandon the sin, feel remorse, resolve never to return to it, and increase in good deeds that wipe out evil deeds. One who repents from a sin is like one who has no sin. "Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'"