The Quran makes an amazing accurate prophecy when it revealed the following:

The Romans have been defeated in the nearer land, and they, after their defeat will be victorious, within a few years. With Allah is the Decision, in the past and in the Future: on that Day shall the Believers rejoice (30:1-4)

So the Quran mentions the fact of the Romans being defeated, and indeed they were defeated by none other than the Persians, In Jerusalem, with the crushing siege of Jerusalem that took place in 614.

Now after mentioning this fact, the Quran goes on to make a statement that even after this defeat; the Romans would be victorious again within a few years. Now the Arabic term that was used for a few years was understood to mean between 3-9 years. So therefore the Quran states that after the Roman defeat, they would be revictorious within 3-9 years.

Now indeed this is a very bold statement to make, because 3-9 years can pass away, and the Romans may never win, therefore this would prove the Quran to be completely wrong, and that it obviously cannot be from the Divine creator. Yet miraculously this prophecy came to pass in 7 years! 7 years after this crushing defeat by the Persians the Romans were finally victorious in the battle of Issus which took place in 622.

The battle of Issus was the start of a Roman counter offensive against the Persians after their crushing defeat, and the Romans finally gained some momentum of their own with a crushing defeat of the Persians in this battle. More remarkable was that this battle was the start of the counter offensive as I just stated, the Byzantines would go on to completely defeat and crush the Persians after the battle of Issus!

Hence the Quran got it completely right! If the Quran was not the Word of God then this prophecy would have failed, yet since the Quran is the Word of God, that is why it made the prophecy in the first place, and why the prophecy was accurately fulfilled. 

And Allah Knows Best!