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Abu Sa'id al-Khudri reported that the Messenger of Allah (ﷺ) said: A group would secede itself (from the Ummah) when there would be dissension among the Muslims. Out of the two groups who would be nearer the truth would kill them.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا شَيْبَانُ بْنُ فَرُّوخَ، حَدَّثَنَا الْقَاسِمُ، - وَهُوَ ابْنُ الْفَضْلِ الْحُدَّانِيُّ - حَدَّثَنَا أَبُو نَضْرَةَ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " تَمْرُقُ مَارِقَةٌ عِنْدَ فُرْقَةٍ مِنَ الْمُسْلِمِينَ يَقْتُلُهَا أَوْلَى الطَّائِفَتَيْنِ بِالْحَقِّ " .
sunnah.com