Abdullah bin Abbas reported,

Regarding the words of Allah the Exalted, "Alif Lam Mim. The Romans have been defeated in the nearest land" [Rum 30:1–3], he said, they were defeated and they were victorious. The polytheists wanted the Persians to triumph over the Romans, because both they and the Persians were idolaters, while the Muslims wanted the Romans to triumph over the Persians, because the Romans were People of the Book.The matter was mentioned to Abu Bakr, and Abu Bakr mentioned it to the Messenger of Allah ﷺ, who said, "The Romans will indeed be victorious."Abu Bakr conveyed this to them, and they said, "Set a term between us and you. If we prevail, we shall have such and such, and if you prevail, you shall have such and such."So he set a term of five years, but the Romans did not prevail within it. They mentioned this to the Prophet ﷺ, and he said, "Why did you not make it less than that?" The narrator said, I think he said, "less than ten."Abu Saeed said, the word "bid" refers to anything less than ten. He said, then the Romans were victorious afterward. He said, that is the meaning of His words, "Alif Lam Mim. The Romans have been defeated" up to His words "and on that day the believers will rejoice at the victory of Allah. He gives victory to whom He wills" [Rum 30:1–5].Sufyan said, I heard that they prevailed over them on the day of Badr.

حدثنا الحسين بن حريث حدثنا معاوية بن عمرو عن أبي إسحق الفزاري عن سفيان الثوري عن حبيب بن أبي عمرة عن سعيد بن جبير

عن ابن عباس

في قول الله تعالى {الم غلبت الروم في أدنى الأرض} قال غلبت وغلبت كان المشركون يحبون أن يظهر أهل فارس على الروم لأنهم وإياهم أهل الأوثان وكان المسلمون يحبون أن يظهر الروم على فارس لأنهم أهل الكتاب فذكروه لأبي بكر فذكره أبو بكر لرسول الله ﷺ قال أما إنهم سيغلبون فذكره أبو بكر لهم فقالوا اجعل بيننا وبينك أجلا فإن ظهرنا كان لنا كذا وكذا وإن ظهرتم كان لكم كذا وكذا فجعل أجلا خمس سنين فلم يظهروا فذكروا ذلك للنبي ﷺ فقال ألا جعلته إلى دون قال أراه العشر قال أبو سعيد والبضع ما دون العشر قال ثم ظهرت الروم بعد قال فذلك قوله تعالى {الم غلبت الروم} إلى قوله {ويومئذ يفرح المؤمنون بنصر الله ينصر من يشاء} قال سفيان سمعت أنهم ظهروا عليهم يوم بدر