Sahih Muslim 1785 a
It has been narrated on the authority of Abu Wa'il who said:
Sahal b. Hunaif stood up on the Day of Siffin and said: O ye people, blame yourselves (for want of discretion) ; we were with the Messenger of Allah (ﷺ) on the Day of Hudaibiya. If we had thought it fit to fight, we could fight. This was in the truce between the Messenger of Allah (ﷺ) and the polytheists. Umar b. Khattab came, approached the Messenger of Allah (ﷺ) and said: Messenger of Allah, aren't we fighting for truth and they for falsehood? He replied: By all means. He asked: Are not those killed from our side in Paradise and those killed. from their side in the Fire? He replied: Yes. He said: Then why should we put a blot upon our religion and return, while Allah has not decided the issue between them and ourselves? He said: Son of Khattab, I am the Messenger of Allah. Allah will never ruin me. (The narrator said): Umar went away, but he could not contain himself with rage. So he approached Abu Bakr and said: 'Abu Bakr, aren't we fighting for truth and they for falsehood? He replied: Yes. He asked: Aren't those killed from our side in Paradise and those killed from their side in the Fire? He replied: Why not? He (then) said: Why should we then disgrace our religion and return while God has not yet decided the issue between them and ourselves? Abu Bakr said: Son of Khattab, verily, he is the Messenger of Allah, and Allah will never ruin him. (The narrator continued): At this (a Sura of) the Qur'an (giving glad tidings of the victory) was revealed to the Messenger of Allah (ﷺ). He sent for Umar and made him read it. He asked: Is (this truce) a victory? He (the Messenger of Allah) replied: Yes. At this Umar was pleased, and returned.
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ نُمَيْرٍ، ح وَحَدَّثَنَا ابْنُ نُمَيْرٍ، - وَتَقَارَبَا فِي اللَّفْظِ - حَدَّثَنَا أَبِي، حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ سِيَاهٍ، حَدَّثَنَا حَبِيبُ بْنُ أَبِي ثَابِتٍ، عَنْ أَبِي وَائِلٍ، قَالَ قَامَ سَهْلُ بْنُ حُنَيْفٍ يَوْمَ صِفِّينَ فَقَالَ أَيُّهَا النَّاسُ اتَّهِمُوا أَنْفُسَكُمْ لَقَدْ كُنَّا مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم يَوْمَ الْحُدَيْبِيَةِ وَلَوْ نَرَى قِتَالاً لَقَاتَلْنَا وَذَلِكَ فِي الصُّلْحِ الَّذِي كَانَ بَيْنَ رَسُولِ اللَّهِ صلى الله عليه وسلم وَبَيْنَ الْمُشْرِكِينَ فَجَاءَ عُمَرُ بْنُ الْخَطَّابِ فَأَتَى رَسُولَ اللَّهِ صلى الله عليه وسلم فَقَالَ يَا رَسُولَ اللَّهِ أَلَسْنَا عَلَى حَقٍّ وَهُمْ عَلَى بَاطِلٍ قَالَ ‏"‏ بَلَى ‏"‏ ‏.‏ قَالَ أَلَيْسَ قَتْلاَنَا فِي الْجَنَّةِ وَقَتْلاَهُمْ فِي النَّارِ قَالَ ‏"‏ بَلَى ‏"‏ ‏.‏ قَالَ فَفِيمَ نُعْطِي الدَّنِيَّةَ فِي دِينِنَا وَنَرْجِعُ وَلَمَّا يَحْكُمِ اللَّهُ بَيْنَنَا وَبَيْنَهُمْ فَقَالَ ‏"‏ يَا ابْنَ الْخَطَّابِ إِنِّي رَسُولُ اللَّهِ وَلَنْ يُضَيِّعَنِي اللَّهُ أَبَدًا ‏"‏ ‏.‏ قَالَ فَانْطَلَقَ عُمَرُ فَلَمْ يَصْبِرْ مُتَغَيِّظًا فَأَتَى أَبَا بَكْرٍ فَقَالَ يَا أَبَا بَكْرٍ أَلَسْنَا عَلَى حَقٍّ وَهُمْ عَلَى بَاطِلٍ قَالَ بَلَى ‏.‏ قَالَ أَلَيْسَ قَتْلاَنَا فِي الْجَنَّةِ وَقَتْلاَهُمْ فِي النَّارِ قَالَ بَلَى ‏.‏ قَالَ فَعَلاَمَ نُعْطِي الدَّنِيَّةَ فِي دِينِنَا وَنَرْجِعُ وَلَمَّا يَحْكُمِ اللَّهُ بَيْنَنَا وَبَيْنَهُمْ فَقَالَ يَا ابْنَ الْخَطَّابِ إِنَّهُ رَسُولُ اللَّهِ وَلَنْ يُضَيِّعَهُ اللَّهُ أَبَدًا ‏.‏ قَالَ فَنَزَلَ الْقُرْآنُ عَلَى رَسُولِ اللَّهِ صلى الله عليه وسلم بِالْفَتْحِ فَأَرْسَلَ إِلَى عُمَرَ فَأَقْرَأَهُ إِيَّاهُ فَقَالَ يَا رَسُولَ اللَّهِ أَوَفَتْحٌ هُوَ قَالَ ‏"‏ نَعَمْ ‏"‏ ‏.‏ فَطَابَتْ نَفْسُهُ وَرَجَعَ ‏.‏