How does a believer fall into major sins, especially adultery, despite his adherence to religion, his knowledge of Allah's boundaries, his recitation of the Quran, and his following of the noble Prophetic Sunnah? And how can he repent from this major sin?

Even though a believer has faith in Allah and the Last Day, and knows the consequences of sins, they may still fall into sin during moments of heedlessness or weak faith. The Prophet, peace and blessings be upon him, said: "The adulterer does not commit adultery while he is a believer."

However, the believer quickly remembers Allah and holds themselves accountable, as Allah Almighty says: "Indeed, those who fear Allah - when an impulse from Satan touches them, they remember [Him] and at once they have insight," and "And those who, when they commit an indecency or wrong themselves [by transgression], remember Allah and ask forgiveness for their sins - and who can forgive sins except Allah? - and [who] do not knowingly persist in what they have done."

So, those whose faith weakens and who fall into sin, then repent, Allah has made them among the righteous. This religion is not harsh on a person who weakens before their desires, as long as they know that they are a servant who errs, and they have a Lord who forgives them, and they acknowledge their servitude to Him and do not act arrogantly regarding their sin.

The path to repentance from any sin, including adultery, is regret, seeking forgiveness, resolving not to return to it, and ceasing to persist in it.