There were two world superpowers at the time, the “Roman” Byzantines, and the Persian Sassanids. The two had begun a massive war with one another, with the Sassanids clearly coming out on top. The Sassanids had taken Byzantine Armenia, Syria, Palestine, Egypt, Libya, Anatolia, and even the Byzantine True Cross artifact. Thus, the Byzantine empire was headed for ruin. They lost everything to the Persian Sassanids in a major war, and hope was low

During this time of absolute loss for the Byzantines, the Qur’an made a bold claim. It stated that the Byzantines would make a huge comeback against the Sassanian's within 3 to 9 years. Imagine the consequences of this. The risk is immense with this claim.

If 9 years pass and this prophecy does not come true, the Prophet ﷺ will be proven to be a false prophet. Does it make sense for a liar to do something so risky?

Here is what Edward Gibbon had to say in “The History of the Decline and Fall of the Roman Empire” about this prophecy:

“At the time when this prediction is said to have been delivered, no prophecy could be more distant from its accomplishment, since the first twelve years of [the Byzantine King] Heraclius announced the approaching dissolution of the [Byzantine] empire.”

The only thing that an ordinary observer could have seen is the Sassanian’s demolishing the Byzantines and the incoming dissolution of the Byzantine empire. Of course, the prophecy did come true despite this. After about 7 years from the Byzantines defeat, they made a huge comeback and started to take back all of the lands they lost. No observer would have expected such a thing to happen, yet the Prophet ﷺ and the Muslims knew otherwise.

This is how much land the Sassanids lost control of by the end of the Byzantine comeback.