Musnad Ahmad 790:106

Abu Kamil and 'Affan narrated to us, they said: Hammad ibn Salamah narrated to us, from Qatadah, from Mutarrif ibn 'Abdullah ibn al-Shikhkhir, from 'Imran ibn Husayn, that the Prophet, peace and blessings of Allah be upon him, said: "A group of my Ummah will continue to fight for the truth, prevailing over those who oppose them, until the last of them fights the False Messiah (al-Masih al-Dajjal)."