Niyar bin Mukram reported,

When the verse "Alif Lam Mim. The Romans have been defeated in the nearest land, and after their defeat they will be victorious within a few years" [Rum 30:1–4] was revealed, the Persians at that time held the upper hand over the Romans. The Muslims wanted the Romans to prevail over them, since the Romans, like themselves, were people of a scripture. This is what Allah refers to in His words, "And on that day the believers will rejoice in the victory granted by Allah. He gives victory to whom He wills, and He is the Mighty, the Merciful" [Rum 30:4–5]. Quraysh, on the other hand, wanted the Persians to prevail, since the Persians, like themselves, possessed no scripture and no belief in the resurrection.So when Allah revealed this verse, Abu Bakr Siddiq went out calling aloud through the districts of Makkah, "Alif Lam Mim. The Romans have been defeated in the nearest land, and after their defeat they will be victorious within a few years" [Rum 30:1–4].Some men of Quraysh said to Abu Bakr, "Then this is a matter to be settled between us and you. Your companion claims the Romans will defeat the Persians within a few years. Shall we not make a wager with you over it?"Abu Bakr replied, "Certainly." This was before wagering was forbidden.So Abu Bakr and the polytheists made their wager and agreed on the stakes. They asked Abu Bakr, "How many years will you set? 'A few years' means anywhere from three to nine. Name a middle figure between us that we can settle on."They fixed six years between them. The six years passed without the Romans prevailing, so the polytheists took the stake Abu Bakr had put up. Then, when the seventh year came, the Romans triumphed over the Persians. The Muslims criticized Abu Bakr for having named six years, since Allah had said, "within a few years" [Rum 30:4]. And at that point a great many people accepted Islam.

عن نيار بن مكرم الأسلمي قال

لما نزلت {الم غلبت الروم في أدنى الأرض وهم من بعد غلبهم سيغلبون في بضع سنين} فكانت فارس يوم نزلت هذه الآية قاهرين للروم، وكان المسلمون يحبون ظهور الروم عليهم لأنهم وإياهم أهل كتاب وفي ذلك قول الله تعالى {ويومئذ يفرح المؤمنون بنصر الله ينصر من يشاء وهو العزيز الرحيم} فكانت قريش تحب ظهور، فارس، لأنهم وإياهم ليسوا بأهل كتاب ولا إيمان ببعث، فلما أنزل الله تعالى هذه الآية، خرج أبو بكرالصديق يصيح في نواحي مكة {الم غلبت الروم في أدنى الأرض وهم من بعد غلبهم سيغلبون في بضع سنين} قال ناس من قريش لأبي بكرفذلك بينا وبينكم، زعم صاحبكم أن الروم ستغلب فارسا في بضع سنين، أفلا نراهنك على ذلك؟ قال: بلى وذلك قبل تحريم الرهان، فارتهن أبو بكر والمشركون، وتواضعوا الرهان، وقالوا لأبي بكر: كم تجعل؟ البضع ثلاث سنين إلى تسع سنين، فسم بيننا وبينك وسطا تنتهي إليه، قال: فسموا بينهم ست سنين قال: فمضت الست سنين قبل أن يظهروا، فأخذ المشركون رهن أبي بكر، فلما دخلت السنة السابعة ظهرت الروم على فارس، فعاب المسلمون على أبي بكر تسمية ست سنين؛ لأن الله تعالى قال {في بضع سنين} قال: وأسلم عند ذلك ناس كثير.