The Messenger of Allah ﷺ said, "You will fight the Arabian Peninsula and Allah will grant you victory over it. Then you will fight Persia and Allah will grant you victory over it. Then you will fight the Romans and Allah will grant you victory over them. Then you will fight the Dajjal and Allah will grant you victory over him."Jabir said, "The Dajjal will not appear until the Romans have been conquered."
حدثنا حسين عن زائدة عن عبد الملك بن عمير وعبد الصمد حدثنا زائدة حدثنا عبد الملك بن عمير
قال رسول الله ﷺ تقاتلون جزيرة العرب فيفتحها الله لكم ثم تقاتلون فارس فيفتحها الله لكم ثم تقاتلون الروم فيفتحها الله لكم ثم تقاتلون الدجال فيفتحه الله لكم قال فقال جابر لا يخرج الدجال حتى يفتتح الروم
Its isnad is sahih. Muslim narrated it, 2:266, at length, and Ibn Majah narrated it, 2:270, in brief, both through Abdul-Malik bin Umayr. This hadith and the one that follows it are not from the musnad of Saad bin Abu Waqqas, but rather from the musnad of his nephew Nafi bin Utbah bin Abu Waqqas, whose musnad will come later at 4:337-338, where this hadith appears with two isnads, one brief and one at length. Nafi bin Utbah was a companion who accepted Islam on the day of the Conquest, and he has no hadith except this one, narrated from him by his cousin Jabir bin Samura.