The Treasures of Khosrau and Caesar
A sound prophecy about the two great imperial powers of the Prophet's age is narrated from Abu Huraira. Its wording is not a direct prophecy of the conquest of the city of Rome, nor a detailed prediction of the final end of the Byzantine Empire. Rather, it speaks of Khosrau (Kisra), ruler of Persia, and Caesar (Qaysar), ruler of the Romans/Byzantines, and foretells that Muslims would come to spend the treasures associated with both in Allah's cause.
Narrated Abu Huraira: Prophet Muhammad (PBUH) said, "When Khosrau perishes, there will be no Khosrau after him, and when Caesar perishes, there will be no Caesar after him. By Him in Whose Hand Muhammad's soul is, you will surely spend the treasures of both of them in Allah's cause."
This narration is reported in Sahih al-Bukhari (numbering varies across editions and platforms) and also in Sahih Muslim with closely related wording. Its authenticity is therefore sahih, but the argument should rest on the established wording rather than on any one modern hadith number.
At the time this prophecy was spoken, the Byzantine Empire and the Sassanid Empire were the two superpowers known to Arabia. The Byzantines, ruled by Caesar from Constantinople, dominated much of the eastern Mediterranean, including Syria-Palestine and Egypt. The Sassanians, ruled by Khosrau in Persia, controlled Iraq and Iran and had recently fought devastating wars with Byzantium. Both empires were under strain, so the point should not be overstated as if they were untouched by weakness; nevertheless, the idea that the small Muslim community of Arabia would inherit and spend the wealth of these imperial powers would still have seemed extraordinary.
In the Persian case, the fulfilment was especially direct. Khosrau II (Parviz), the Sassanid ruler during the Prophet's lifetime, was overthrown and killed in 628 CE, after which Persia suffered rapid succession crises and civil conflict. Within the generation of the Companions, the Muslim armies defeated the Sassanids in decisive campaigns, entered al-Mada'in, and the Sassanid state effectively ended with the death of Yazdegerd III in 651 CE. The Persian imperial office of Khosrau did not continue as a real sovereign power, and its wealth came into Muslim hands.
The Byzantine case needs a more careful reading. The Roman/Byzantine imperial title did continue in Constantinople for centuries after the Prophet Muhammad (PBUH), so the hadith should not be presented as saying that no emperor called Caesar would ever exist again. Classical commentators explained the wording in light of what actually occurred: Caesar's rule was removed from al-Sham and the eastern provinces that had been central to his power, while Persia's monarchy disappeared altogether. Under the Rashidun conquests, Muslim forces took Syria-Palestine and Egypt from Byzantine rule, and later North Africa; the wealth, revenues, and spoils of these former imperial lands entered the Muslim polity and were spent in public and military causes. The Ottoman conquest of Constantinople in 1453 is a separate later event and is not necessary to establish the meaning of this particular hadith.
For a fair-minded reader, the strength of the prophecy lies in its scale and timing: a persecuted Arabian community was told that it would come to dispose of the treasures of the two great imperial powers. A sceptical reader may rightly note that the Byzantine-Sassanid wars had exhausted both empires, which makes some future upheaval imaginable. Even so, the specific outcome that followed within a generation--the end of the Sassanid imperial order and the removal of Caesar's authority from Syria-Palestine and Egypt, with their wealth passing into Muslim hands--was far from an obvious political prediction.
It is therefore important to state the claim precisely. This hadith is a strong report about the loss of Khosrau's sovereignty and Caesar's loss of his eastern treasures and provinces, not a stand-alone proof for the conquest of the city of Rome or a detailed map of Byzantine history. It gives no dates and does not flatten the complex military, economic, and political causes behind the conquests. Read with these qualifications, it remains a serious prophetic sign without requiring exaggerated claims.