Musnad Abu Ya'la al-Mawsili 42:301

Zuhayr narrated to us, Muhammad ibn Abd Allah al-Asadi narrated to us, Sufyan narrated to us, from Habib ibn Abi Thabit, from al-Dahhak al-Mashriqi, from Abu Sa’id, from the Prophet (may Allah bless him and grant him peace), in a hadith in which he mentioned a people who would emerge upon a differing faction of people; the closer of the two factions to the truth would kill them.