Musnad Ahmad 31:905

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from 'Ali ibn Zayd, from Abu Nadra, who said: I heard Abu Sa'id al-Khudri, that he heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "The Hour will not be established until two great groups fight each other, their claim is one, and a renegade group (mariqa) will emerge between them, which the one of the two groups that is closer to the truth will kill."