Abu Sa'id al-Khudri reported from the Apostle of Allah (ﷺ) that a group (Khwarij) would emerge from the different parties (the party of Hadrat 'Ali and the party of Amir Mu'awiyah), the group nearer the truth between the two would kill them.
Hadith ReferenceSahih Muslim / The Book of Zakat / Hadith: 1064