All praise is due to Allah, and peace and blessings be upon our Prophet Muhammad.
A Muslim strives to please Allah in all their affairs by doing what Allah has commanded and avoiding what Allah has forbidden. However, a Muslim may sometimes slip up or become negligent, leading them to commit a sin and disobey Allah's law. If a person does something like this, they should immediately seek forgiveness and repent. The Quran has clarified the situation of a Muslim who commits sins, as Allah says {what means}: "Say, "O My servants who have transgressed against themselves [by sinning], do not despair of Allah's mercy. Indeed, Allah forgives all sins. Indeed, He is the Forgiving, the Merciful." [Az-Zumar, 53].
Indeed, sin is fundamentally a cause of Allah’s wrath and warrants punishment in the Hereafter. It may also affect a person's life in this world, causing them to become unsettled in their behavior and relationships with others, and preventing success in their actions and time, whether they are aware of this or not. For this reason, Allah has prescribed for us many ways in Islam to repent from sins and make amends for what has passed.
If the sin committed by the servant is a major one, such as apostasy, fornication, usury, drinking alcohol, disobedience to parents, slander of chaste women, murder, or consuming the wealth of an orphan, then it is an individual obligation upon them to repent from it. True repentance consists of three essential actions: to immediately cease committing the sin, to resolve never to return to it as best as possible, and to feel sincere remorse in the heart for the wrong done, seeking forgiveness from Allah. If they do this, Allah will forgive them as He has promised. Allah says {what means}: "And it is He who accepts repentance from His servants and pardons misdeeds, and He knows what you do" [Ash-Shura, 25]. Additionally, if the sin involves violating the rights of others, such as taking someone's wealth, it is obligatory to return the right to its owner.
As for minor sins, Allah, in His mercy and grace, has provided many ways to seek forgiveness. If He willed, He would not have forgiven anything. Allah says {what means}: 'And whatever affliction befalls you - it is for what your hands have earned. And He pardons much.' [Ash-Shura, 30]. Among these ways are: repenting according to the conditions mentioned previously, performing ablution properly, walking to the mosque, prostrating, fasting during Ramadan, performing night prayers, and avoiding major sins.
As evidence for this, Allah says {what means}: 'If you avoid the major sins which you are forbidden, We will wipe out your evil deeds and admit you to a noble entrance.' [An-Nisa, 31]. Moreover, the Messenger of Allah, peace be upon him, said: 'Shall I not inform you of that which erases sins and raises degrees?' They said, 'Yes, O Messenger of Allah.' He said, 'Performing ablution completely, despite its difficulty, going to the mosques frequently, and waiting for the next prayer after the prayer, for that is the stationing (of the soldiers).' (Reported by Muslim). He also said, 'There is no Muslim who performs a prescribed prayer, and perfects its ablution, humility, bowing, except that it will be an expiation for the sins committed before it, as long as he has not committed a major sin, for his entire life.' (Reported by Muslim)."
Scholars of Islamic law have mentioned that persistence in committing minor sins can elevate them to the level of major sins. This is because persisting in sin demonstrates carelessness and a lack of concern. Therefore, a Muslim should strive to consistently repent from every sin, avoid repeating wrongdoings, and never tire of seeking forgiveness, no matter how often they may fall into sin. Moreover, one should never despair of Allah’s mercy, for despair is itself a sin. To despair implies that one belittles Allah’s mercy and His immense grace.
No matter the sin, minor or major, a Muslim commits, Allah forgives it through sincere repentance. It is impermissible to declare Muslims as disbelievers because of their sins, regardless of the nature of those sins. Indeed, the one who repents from sin is like someone who has no sin. Declaring Muslims disbelievers due to their sins is the doctrine of the Khawarij, a misguided sect whose views are not valid in Islamic law. It is stated in Tuhfat al-Muhtaj (3/92): "... Every Muslim, even a sinner, will enter Paradise, even if after a prolonged punishment. This is in opposition to the view held by many misguided sects, such as the Mu'tazilites and the Khawarij."
In conclusion, a Muslim who commits a sin is a believer and not a disbeliever. It is obligatory for him, according to Islamic law, to repent from his sin, resolve not to fall into it again, and return the rights to their rightful owners. If he falls into sin again, he should return to repentance and renew his covenant of servitude to Allah. He should never despair due to his sins, for the one who repents from a sin is like one who has no sin at all.
Whoever dies without having repented from their sin is under the will of Allah. If He wills, He may forgive him, and if He wills, He may punish him. Al-Luqani, may Allah have mercy on him, said in "Jawharat al-Tawhid":
"Whoever dies without having repented from their sin, their matter is entrusted to their Lord." And Allah The Almighty knows best.
