Musnad Ahmad 716:2

Mu'awiyah ibn 'Amr narrated to us, Abu Ishaq—meaning al-Fazari—narrated to us, from 'Abd al-Malik ibn 'Umayr, from Jabir ibn Samurah, from Nafi' ibn 'Utbah, who said: I was with the Messenger of Allah, peace and blessings of Allah be upon him, on a military expedition. A people came to him from the direction of the west, wearing wool garments. They met him at a hillock, and they were standing while he was sitting. I went to him and stood between them and him, and I memorized from him four words which I count on my hand. He said: "You will fight the Arabian Peninsula, and Allah will open it. Then you will fight Persia, and Allah will open it. Then you will fight the Romans, and Allah will open it. Then you will fight the Dajjal, and Allah will open him." Nafi' said: "O Jabir, do you not see that the Dajjal will not emerge until the Romans are opened?"