Mustadrak al-Hakim — Hadith 3582

It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Muslims wanted the Romans to prevail over the Persians because they were People of the Book, while the polytheists wanted the Persians to prevail over the Romans because they were idol-worshippers. The Muslims mentioned this to Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him), and he informed the Prophet (peace and blessings be upon him) of it. The Prophet (peace and blessings be upon him) said to him: "Know that they (the Persians) will soon be defeated." Sayyiduna Abu Bakr (may Allah be pleased with him) mentioned this to the polytheists, and they said: "Set a term between us and you: if they prevail, you will get such-and-such, and if we win, we will get such-and-such." So he set a term of five years, but within it the Romans did not prevail. Sayyiduna Abu Bakr (may Allah be pleased with him) mentioned this to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said: "Why did you not set the term at less than ten (that is, up to nine years)?" The narrator says: After that the Romans prevailed, and this is the saying of Allah, the Mighty and Majestic: "Alif Lam Mim. The Romans have been defeated in the nearest land, but after their defeat they will prevail" [Surah al-Rum: 1-3], meaning that the Romans were first defeated and then later prevailed; "To Allah belongs the command before and after, and on that day the believers will rejoice at the help of Allah" [Surah al-Rum: 4]. Sufyan says: I have heard that they (the Romans) prevailed (over the Persians) on the very day of Badr.
This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it.