Abu `Isa At-Tirmidhi recorded that Niyar bin Mukram Al-Aslami said: "When the following Ayat were revealed:

﴿الم - غُلِبَتِ الرُّومُ - فِي أَدْنَى الأَرْضِ وَهُم مِّنْ بَعْدِ غَلَبِهِمْ سَيَغْلِبُونَ ﴾

(Alif Lam Mim. The Romans have been defeated. In the nearest land, and they, after their defeat, will be victorious. In Bid` years.) on the day they were revealed, the Persians were prevailing over the Romans. The Muslims wanted the Romans to prevail over them (the Persians), because they were both people who followed a Book. Concerning this Allah said:

﴿فِى بِضْعِ سِنِينَ لِلَّهِ الاٌّمْرُ مِن قَبْلُ وَمِن بَعْدُ وَيَوْمَئِذٍ يَفْرَحُ الْمُؤْمِنُونَ - بِنَصْرِ اللَّهِ يَنصُرُ مَن يَشَآءُ وَهُوَ الْعَزِيزُ الرَّحِيمُ ﴾

(And on that day, the believers will rejoice -- with the help of Allah. He helps whom He wills, and He is the All-Mighty, the Most Merciful.) The Quraysh, on the other hand, wanted the Persians to prevail, because neither of them were people who followed a Book and neither of them believed in the Resurrection. When Allah revealed these Ayat, Abu Bakr went out proclaiming throughout Makkah:

﴿الم - غُلِبَتِ الرُّومُ ﴾

(Alif Lam Mim. The Romans have been defeated. In the nearest land, and they, after their defeat, will be victorious. In Bid` years.) Some of the Quraysh said to Abu Bakr: `This is (a bet) between us and you. Your companion claims that the Romans will defeat the Persians within three to nine years, so why not have a bet on that between us and you' Abu Bakr said, `Yes.' This was before betting had been forbidden. So, Abu Bakr and the idolators made a bet, and they said to Abu Bakr: `What do you think, Bid` means something between three and nine years, so let us agree on the middle.' So they agreed on six years. Then six years passed without the Romans being victorious, so the idolators took what they had bet with Abu Bakr. When the seventh year came and the Romans were finally victorious over the Persians, the Muslims rebuked Abu Bakr for agreeing on six years. He said: `Because Allah said: "In Bid` years.''' At that time, many people became Muslim.'' This is how it was narrated by At-Tirmidhi, then he said, "This is a Hasan Hadith.''