Allah commands His Prophet Muhammad ,
قُل لِلَّذِينَ كَفَرُواْ إِن يَنتَهُواْ
(Say to those who have disbelieved, if they cease...) the disbelief, defiance and stubbornness they indulge in, and embrace Islam, obedience and repentance.
يُغْفَرْ لَهُمْ مَّا قَدْ سَلَفَ
(their past will be forgiven.) along with their sins and errors. It is recorded in the Sahih Al-Bukhari that Abu Wa'il said that Ibn Mas'ud said that the Messenger of Allah ﷺ said,
«مَنْ أَحْسَنَ فِي الْإِسْلَامِ لَمْ يُؤَاخَذْ بِمَا عَمِلَ فِي الْجَاهِلِيَّةِ، وَمَنْ أَسَاءَ فِي الْإِسْلَامِ أُخِذَ بِالْأَوَّلِ وَالْآخِر»
(He who becomes good in his Islam, will not be punished for what he has committed during Jahiliyyah (before Islam). He who becomes bad in his Islam, will face a punishment for his previous and latter deeds.)
It is also recorded in the Sahih that the Messenger of Allah ﷺ said,
«الْإِسْلَامُ يَجُبُّ مَا قَبْلَهُ وَالتَّوْبَةُ تَجُبُّ مَا كَانَ قَبْلَهَا»
("Islam erases what occurred before it, and repentance erases what occurs before it.")
Allah said,
وَإِن يَعُودُواْ
(But if they return, ) and remain on their ways,
فَقَدْ مَضَتْ سُنَّتُ الاٌّوَّلِينِ
(then the examples of those (punished) before them have already preceded.) 8:38 meaning, Our way with the nations of old is that when they disbelieve and rebel, We send down to them immediate torment and punishment.
Allah said,
وَقَـتِلُوهُمْ حَتَّى لاَ تَكُونَ فِتْنَةٌ وَيَكُونَ الدِّينُ كُلُّهُ لِلهِ
(And fight them until there is no more Fitnah, and the religion will all be for Allah alone.)
Al-Bukhari recorded that a man came to Ibn `Umar and said to him, "O Abu `Abdur-Rahman! Why do you not implement what Allah said in His Book,
وَإِن طَآئِفَتَانِ مِنَ الْمُؤْمِنِينَ اقْتَتَلُواْ
(And if two parties (or groups) among the believers fall to fighting...)49:9. What prevents you from fighting as Allah mentioned in His Book" Ibn `Umar said, "O my nephew! I prefer that I be reminded with this Ayah rather than fighting, for in the latter case, I will be reminded by the Ayah in which Allah, the Exalted and Most Honored, said,
وَمَن يَقْتُلْ مُؤْمِناً مُّتَعَمِّداً
(And whoever kills a believer intentionally...) 4:93"
The man said, "Allah, the Exalted, said,
وَقَـتِلُوهُمْ حَتَّى لاَ تَكُونَ فِتْنَةٌ
(And fight them until there is no more Fitnah...)." Ibn `Umar said, "We did that during the time of the Messenger of Allah ﷺ, when Islam was weak and the man would be tried in religion, either tormented to death or being imprisoned. When Islam became stronger and widespread, there was no more Fitnah." When the man realized that Ibn `Umar would not agree to what he is saying, he asked him, "What do you say about `Ali and `Uthman" Ibn `Umar replied, "What do I say about `Ali and `Uthman! As for `Uthman, Allah has forgiven him, but you hate that Allah forgives him. As for `Ali, he is the cousin of the Messenger of Allah ﷺ and his son-in-law," and he pointed with his hand saying, "And this is his house over there." Sa`id bin Jubayr said, "Ibn `Umar came to us and was asked, "What do you say about fighting during Fitnah" Ibn `Umar said, "Do you know what Fitnah refers to Muhammad was fighting against the idolators, and at that time, attending (or residing with) the idolators was a Fitnah (trial in religion). It is nothing like what you are doing, fighting to gain leadership!" All these narrations were collected by Al-Bukhari, may Allah the Exalted grant him His mercy. Ad-Dahhak reported that Ibn `Abbas said about the Ayah,
وَقَـتِلُوهُمْ حَتَّى لاَ تَكُونَ فِتْنَةٌ
(And fight them until there is no more Fitnah...) "So that there is no more Shirk." Similar was said by Abu Al-`Aliyah, Mujahid, Al-Hasan, Qatadah, Ar-Rabi` bin Anas, As-Suddi, Muqatil bin Hayyan and Zayd bin Aslam. Muhammad bin Ishaq said that he was informed from Az-Zuhri, from `Urwah bin Az-Zubayr and other scholars that
حَتَّى لاَ تَكُونَ فِتْنَةٌ
(until there is no more Fitnah) the Fitnah mentioned here means, until no Muslim is persecuted so that he abandons his religion. Ad-Dahhak reported that Ibn `Abbas said about Allah's statement,
وَيَكُونَ الدِّينُ كُلُّهُ لِلهِ
(and the religion (worship) will all be for Allah alone.) "So that Tawhid is practiced in sincerity with Allah." Al-Hasan, Qatadah and Ibn Jurayj said,
وَيَكُونَ الدِّينُ كُلُّهُ لِلهِ
(and the religion will all be for Allah alone) "So that La ilaha illa-llah is proclaimed." Muhammad bin Ishaq also commented on this Ayah, "So that Tawhid is practiced in sincerity towards Allah, without Shirk, all the while shunning all rivals who (are being worshipped) besides Him."
`Abdur-Rahman bin Zayd bin Aslam said about,
وَيَكُونَ الدِّينُ كُلُّهُ لِلهِ
(and the religion will all be for Allah alone) "So that there is no more Kufr (disbelief) with your religion remains." There is a Hadith collected in the Two Sahihs that testifies to this explanation. The Messenger of Allah ﷺ said,
«أُمِرْتُ أَنْ أُقَاتِلَ النَّاسَ، حَتَّى يَقُولُوا: لَا إِلَهَ إِلَّا اللهُ، فَإِذَا قَالُوهَا عَصَمُوا مِنِّي دِمَاءَهُمْ وَأَمْوَالَهُمْ، إِلَّا بِحَقِّهَا، وَحِسَابُهُمْ عَلَى اللهِ عَزَّ وَجَل»
(I was commanded to fight against the people until they proclaim, `There is no deity worthy of worship except Allah.' If and when they say it, they will preserve their blood and wealth from me, except for its right (Islamic penal code), and their reckoning is with Allah, the Exalted and Most Honored.)
Also, in the Two Sahihs, it is recorded that Abu Musa Al-Ash`ari said, "The Messenger of Allah ﷺ was asked about a man who fights because he is courageous, in prejudice with his people, or to show off. Which of these is for the cause of Allah He said,
«مَنْ قَاتَلَ لِتَكُونَ كَلِمَةُ اللهِ هِيَ الْعُلْيَا فَهُوَ فِي سَبِيلِ اللهِ عَزَّ وَجَل»
(Whoever fights so that Allah's Word is the supreme, is in the cause of Allah, the Exalted and Most Honored.)"
Allah said next,
فَإِنِ انْتَهَوْاْ
(But if they cease), and desist from their Kufr as a result of your fighting them, even though you do not know the true reasons why they did so,
فَإِنَّ اللَّهَ بِمَا يَعْمَلُونَ بَصِيرٌ
(then certainly, Allah is All-Seer of what they do.)
Allah said in similar Ayah,
فَإِن تَابُواْ وَأَقَامُواْ الصَّلَوةَ وَءاتَوُاْ الزَّكَوةَ فَخَلُّواْ سَبِيلَهُمْ
(But if they repent and perform the Salah, and give Zakah, then leave their way free.) 9:5,
فَإِخوَانُكُمْ فِى الدِّينِ
(...then they are your brethren in religion.) 9:11, and,
وَقَـتِلُوهُمْ حَتَّى لاَ تَكُونَ فِتْنَةٌ وَيَكُونَ الدِّينُ للَّهِ فَإِنِ انتَهَواْ فَلاَ عُدْوَنَ إِلاَّ عَلَى الظَّـلِمِينَ
(And fight them until there is no more Fitnah and the religion (worship) is for Allah (alone). But if they cease, let there be no transgression except against the wrongdoers.) 2:193
It is recorded in the Sahih that the Messenger of Allah ﷺ said to Usamah bin Zayd when he overpowered a man with his sword, after that man proclaimed that there is no deity worthy of worship except Allah;
«أَقَتَلْتَهُ بَعْدَ مَا قَالَ لَا إِلَهَ إِلَّا اللهُ؟ وَكَيْفَ تَصْنَعُ بِلَا إِلَهَ إِلَّا اللهُ يَوْمَ الْقِيَامَةِ؟»
(Have you killed him after he proclaimed, `La Ilaha Illallah' What would you do with regard to `La Ilaha Illallah' on the Day of Resurrection.)
Usamah said, "O Allah's Messenger! He only said it to save himself." The Messenger ﷺ replied,
«هَلَّا شَقَقْتَ عَنْ قَلْبِهِ؟»
(Did you cut his heart open)
The Messenger ﷺ kept repeating,
«مَنْ لَكَ بِلَا إِلهَ إِلَّا اللهُ يَوْمَ الْقِيَامَةِ؟»
(What would you do with regard to `La Ilaha Illallah' on the Day of Resurrection) until Usamah said, "I wished I had embraced Islam only that day." Allah said next,
وَإِن تَوَلَّوْاْ فَاعْلَمُواْ أَنَّ اللَّهَ مَوْلاَكُمْ نِعْمَ الْمَوْلَى وَنِعْمَ النَّصِيرُ
(And if they turn away, then know that Allah is your protector, an excellent protector, and an excellent helper!)
Allah says, if the disbelievers persist in defying and fighting you, then know that Allah is your protector, master and supporter against your enemies. Verily, what an excellent protector and what an excellent supporter.