Musnad Abu Ya'la al-Mawsili 42:63

'Abd al-Wahid ibn Ghiyath narrated to us, Abu 'Awanah narrated to us, from Qatadah, from Abu Nadrah, from Abu Sa'id, from the Messenger of Allah (may Allah bless him and grant him peace), who said: "There will be two factions from my Ummah. A renegade group will emerge from them, and the one among the two [factions] that is closer to the truth will be responsible for killing them."