Praise be to Allah.
If believers die believing in Allaah but having committed sins less than major shirk that puts a person beyond the pale of Islam, one of two scenarios may apply:
1 – they repented from those sins during their lives. If they repented sincerely, Allaah will accept that from them, and they will once again become like those who did not commit any sin, and they will not be punished for their sins in the Hereafter. Indeed, their Lord may honour them and turn their bad deeds (sayi’aat) into good deeds (hasanaat).
2 – those who die without having repented from their sins, or whose repentance was imperfect and did not meet the required conditions, or their repentance was not accepted. What is proven in the verses of the Qur’aan and the Sunnah of the Prophet, and on which the righteous salaf was agreed is that these – the sinners among those who believe in Tawheed (the oneness of Allaah) – fall into three categories:
The first category: People who have many hasanaat (good deeds) to their credit, which outweigh these sayi’aat (bad deeds). Allaah will forgive them for their bad deeds and admit them to Paradise. The Fire will never touch them, as a kindness and blessing from Allaah. According to a hadeeth narrated by Ibn ‘Umar (may Allaah be pleased with him), the Prophet (peace and blessings of Allaah be upon him) said: “Allaah will bring the believer close and will shelter him with His screen, then He will say, ‘Do you remember such and such a sin? Do you remember such and such a sin?’ and he will say, ‘Yes, O Lord,’ until He makes him confess his sins and he thinks that he is doomed. Then [Allaah] will say, ‘I concealed it for you in the world and I forgive you for it today.’ Then he will be given the book of his good deeds (hasanaat). But as for the kaafir and the hypocrite, the witnesses will say, ‘These are the ones who lied against their Lord!’ No doubt! the curse of Allaah is upon the zaalimoon (wrongdoers) [cf. Hood 11:18].’” (Narrated by al-Bukhaari, 2441; Muslim, 2768).
Allaah says (interpretation of the meaning):
“So as for those whose Scale (of good deeds) will be heavy, they will be the successful (by entering Paradise)”[al-A’raaf 7:8]
“Then as for him whose Balance (of good deeds) will be heavy,
He will live a pleasant life (in Paradise)”[al-Qaari’ah 101:6-7]
The second category: people whose hasanaat and sayi’aat are equal, so their sayi’aat are enough to keep them away from Paradise, but their hasanaat are enough to save them from Hell. These are the people of al-A’raaf (a wall with elevated places) whom Allaah says will stand between Paradise and Hell as long as Allaah wills, then they will be granted permission to enter Paradise, as Allaah says after telling us of the entrance of the people of Paradise to Paradise and the people of Hell to Hell. Allaah says (interpretation of the meaning):
“And between them will be a (barrier) screen and on Al-A‘raaf (a wall with elevated places) will be men (whose good and evil deeds would be equal in Scale), who would recognise all (of the Paradise and Hell people), by their marks (the dwellers of Paradise by their white faces and the dwellers of Hell by their black faces). And they will call out to the dwellers of Paradise, ‘Salaamun ‘Alaykum’ (peace be on you), and at that time they (men on Al-A‘raaf) will not yet have entered it (Paradise), but they will hope to enter (it) with certainty.
And when their eyes will be turned towards the dwellers of the Fire, they will say: ‘Our Lord! Place us not with the people who are Zaalimoon (polytheists and wrongdoers).’
And the men on Al-A‘raaf (the wall) will call unto the men whom they would recognise by their marks, saying: ‘Of what benefit to you were your great numbers (and hoards of wealth), and your arrogance (against Faith)?’
Are they those, of whom you swore that Allaah would never show them mercy. (Behold! It has been said to them): ‘Enter Paradise, no fear shall be on you, nor shall you grieve’”[al-A’raaf 7:46-39]
The third category: People who will meet Allaah persisting in committing major sins and acts of immorality, so their sayi’aat will outweigh their hasanaat. These are the ones who will deserve to enter Hell in a manner commensurate with their sins. Some of them will be seized by the Fire as far as their ankles, some up to mid-calf, some up to their knees, and for some only the mark of sujood will be spared. These are the ones whom Allaah will permit to be brought forth from the Fire because of the intercession of the Prophet (peace and blessings of Allaah be upon him). He, all the Prophets, the angels, the believers and whoever else Allaah wishes to honour will intercede for them. Whoever among these sinners has more faith and committed less sins will have a lighter punishment and remain in Hell for a shorter period and will be brought forth sooner. Those whose sins were greater and whose faith was weaker, will have a greater punishment and will remain for longer. We ask Allaah to keep us safe and sound from all evils.
This is the situation of the sinful believers in the Hereafter.
With regard to this world, so long as they do not do anything that would put them beyond the pale of Islam, then they are believers whose faith is lacking, as the righteous salaf agreed, basing that on the verses of the Qur’aan and the ahaadeeth of the Prophet. These aayahs include:
“But if the killer is forgiven by the brother (or the relatives) of the killed against blood money, then adhering to it with fairness and payment of the blood money to the heir should be made in fairness”
[al-Baqarah 2:178 – interpretation of the meaning]
So Allaah describes the killer as the brother of the heirs of the victim. This brotherhood is the brotherhood of faith, which indicates that the killer is not regarded as a kaafir, even though killing a believer is one of the most serious of major sins.
And Allaah says (interpretation of the meaning):
“And if two parties (or groups) among the believers fall to fighting, then make peace between them both. But if one of them outrages against the other, then fight you (all) against the one that which outrages till it complies with the Command of Allaah. Then if it complies, then make reconciliation between them justly, and be equitable. Verily, Allaah loves those who are the equitable.
The believers are nothing else than brothers (in Islamic religion). So make reconciliation between your brothers, and fear Allaah, that you may receive mercy”[al-Hujuraat 49:9-10]
So Allaah described each of the fighting parties as believers, even though fighting is a major sin. Indeed, He described the ones who reconcile between them as being their brothers, which indicates that the one who commits a major sin which does not reach the degree of shirk and kufr is still regarded as a believer and comes under the rulings on believers, but he is lacking in faith. In this way the shar’i texts may be reconciled and support one another. And Allaah knows best.
See A’laam al-Sunnah al-Manshoorah, 212; Sharh al-‘Aqeedah al-Waasitiyyah by Shaykh Ibn ‘Uthaymeen, 2/238.