Musnad Ahmad 31:208

Yahya narrated to us, from ‘Awf, Abu Nadra narrated to us, from Abu Sa’id, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "My Ummah will split into two factions, and a renegade group will emerge between them, which will be killed by the faction that is closer to the truth."