Musnad Ahmad 31:757

Muhammad ibn Ja'far narrated to us, 'Awf narrated to us, from Abu Nadra, from Abu Sa'id al-Khudri, from the Prophet, peace and blessings of Allah be upon him, who said: "My nation will split into two factions, and a renegade group will emerge from between them. The faction that is closer to the truth will kill them."