Musnad Ahmad 25:910

Mu'awiyah narrated to us, Abu Ishaq narrated to us, from Sufyan, from Habib ibn Abi 'Amrah, from Sa'id ibn Jubayr, from Ibn 'Abbas, who said: The Muslims used to love for the Romans to prevail over the Persians, because they were People of the Book, and the polytheists used to love for the Persians to prevail over the Romans, because they were idolaters. The Muslims mentioned that to Abu Bakr, and Abu Bakr mentioned that to the Messenger of Allah, may Allah bless him and grant him peace. The Prophet, may Allah bless him and grant him peace, said to him: "As for them, they will be defeated." Abu Bakr mentioned that to them, and they said: "Set a time limit between us and you. If they prevail, you shall have such and such, and if we prevail, we shall have such and such." So he set a time limit between them of five years, but they did not prevail. Abu Bakr mentioned that to the Prophet, may Allah bless him and grant him peace, and he said: "Why did you not make it—I think he said:—less than ten?" Sa'id said: "The *bid'* (a few) is what is less than ten." He said: Then the Romans prevailed after that. That is the saying of the Exalted: "Alif-Lam-Mim. The Romans have been defeated. In the nearest land, but they, after their defeat, will overcome. Within a few years" [Ar-Rum: 2-4]. He said: The Romans were defeated, then they prevailed afterward. He said: "To Allah belongs the command, before and after; and that day the believers will rejoice in the victory of Allah" [Ar-Rum: 4]. He said: The believers will rejoice in the victory of Allah.