Sahih Muslim , Book 5, Hadith 2326 (USC-MSA) ⓘ

Abu Sa'id al-Khudri reported Allah's Messenger as saying: There would be two groups in my Ummah, and there would emerge another group (seceding itself from both of them), and the party nearer to the truth among the two would kill them (the group of the Khawarij).

حَدَّثَنَا أَبُو الرَّبِيعِ الزَّهْرَانِيُّ، وَقُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ قُتَيْبَةُ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ قَتَادَةَ، عَنْ أَبِي نَضْرَةَ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ تَكُونُ فِي أُمَّتِي فِرْقَتَانِ فَتَخْرُجُ مِنْ بَيْنِهِمَا مَارِقَةٌ يَلِي قَتْلَهُمْ أَوْلاَهُمْ بِالْحَقِّ ‏" ‏ ‏.‏

It was narrated from Abu Sa'eed Al-Khudri that the Messenger of Allah said: "A group will secede at a time of division among the people, and they will be killed by the group that is closer to the truth."

حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا عَبْدُ الأَعْلَى، حَدَّثَنَا دَاوُدُ، عَنْ أَبِي نَضْرَةَ، عَنْ أَبِي، سَعِيدٍ الْخُدْرِيِّ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ تَمْرُقُ مَارِقَةٌ فِي فُرْقَةٍ مِنَ النَّاسِ فَيَلِي قَتْلَهُمْ أَوْلَى الطَّائِفَتَيْنِ بِالْحَقِّ ‏" ‏ ‏.‏