Sahih Muslim , Book 41, Hadith 6902 (USC-MSA) ⓘ
Abu Huraira reported Allah's Messenger many ahadith and one of them was this: The last Hour will not come until the two parties (of Muslims) confront each other and there is a large-scale massacre amongst them and the claim of both of them is the same.
وَحَدَّثَنَا مُحَمَّدُ بْنُ رَافِعٍ، حَدَّثَنَا عَبْدُ الرَّزَّاقِ، حَدَّثَنَا مَعْمَرٌ، عَنْ هَمَّامِ بْنِ مُنَبِّهٍ، قَالَ هَذَا مَا حَدَّثَنَا أَبُو هُرَيْرَةَ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم فَذَكَرَ أَحَادِيثَ مِنْهَا وَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لاَ تَقُومُ السَّاعَةُ حَتَّى تَقْتَتِلَ فِئَتَانِ عَظِيمَتَانِ وَتَكُونُ بَيْنَهُمَا مَقْتَلَةٌ عَظِيمَةٌ وَدَعْوَاهُمَا وَاحِدَةٌ " .
also referenced under: Book 54, Hadith 22 (In-Book) & Hadith 157 (Reference)