Jami` at-Tirmidhi: Book 47, Hadith 246

Narrated Niyar bin Mukram Al-Aslami: “When (the following) was revealed: ‘Alif Lam Mim. The Romans have been defeated. In the nearest land, and they, after their defeat, will be victorious in Bid’ years (30:1-4).’ – on the day that these Ayat were revealed, the Persians had defeated the Romans, and the Muslims had wanted the Romans to be victorious over them, because they were the people of the Book. So Allah said about that: ‘And on that day, the believers will rejoice – with the help of Allah. He helps whom He wills, and He is the Almighty, the Most Merciful (30:4 & 5). The Quraish wanted the Persians to be victorious since they were not people of the Book, nor did they believe in the Resurrection. So when Allah revealed these Ayat, Abu Bakr As-Siddiq, may Allah be pleased with him, went out, proclaiming throughout Makkah: ‘Alif Lam Mim. The Romans have been defeated. In the nearest land, and they, after their defeat, will be victorious, in Bid’ years (30:1-4).’ Some of the Quraish said: ‘Then this is (a bet) between us and you. Your companion claims that the Romans will defeat the Persians in Bid’ years, so why have have a bet on that between us and you?’ Abu Bakr said: ‘Yes.’ This was before betting has been forbidden. So Abu Bakr and the idolaters 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. The idolaters took what they won in the bet from Abu Bakr. When the seventh year came and the Romans were finally victorious over the Persians, the Muslims rebuked Abu Bakr for agreeing to six years. He said: ‘Because Allah said: ‘In Bid’ years.’ At that time, many people became Muslims.”