Musnad Ahmad 31:426

Bahz narrated to us, Abu 'Awanah narrated to us, from Qatadah, from Abu Nadrah, from Abu Sa'id, from the Prophet, peace and blessings of Allah be upon him, who said: "My Ummah will be two factions; a renegade group will emerge between them, and the one among the two factions that is closer to the truth will be responsible for killing them."