Muslim conquest of Persia
Persian rebellion and reconquest

Umar was assassinated in November 644 by a Persian slave named Abu Lu'lu'a Firuz, after having refused to lift a tax imposed upon the latter. Soon after, Abu Lu'lu'a's was either executed or committed suicide. In retaliation, Ubayd Allah ibn Umar (one of Umar's sons) killed Abu Lu'lu'a's daughter, and declared his intention to kill all non-Arabs residing in Medina. Acting upon a claim that they had been seen conspiring with Abu Lu'lu'a while he was holding the murder weapon, Ubayd Allah killed Hurmuzān, an ex- Sasanian military officer who had been working for Umar as an adviser after his capture by the Muslims, and Jufayna, a Christian man from the city of Al-Hira in Iraq who had been taken to Medina to serve as a tutor. Just like Abu Lu'lu'a's assassination of Umar over something as trivial as a tax burden, Ubayd Allah's retaliatory killing of apparently random non-Arabs bears witness to the strong tensions that existed between Arabs and non-Arabs in the early Islamic caliphate.

Uthman ibn Affan (644–656) succeeded Umar as caliph. During his reign, almost the whole of the former Sassanid empire's territory rebelled from time to time, requiring him to send several military expeditions to crush the rebellions and recapture Persia and its vassal states. The main rebellions were in the Persian provinces of Armenia, Azerbaijan, Fars, Sistan (in 649), Khorasan (651), and Makran (650). Finally, in 651, Yazdegerd III, the last Sassanid emperor, was killed near Merv by a local miller for his purse, thus putting an end to both his dynasty and to organized Persian resistance. Meanwhile, Uthman's empire expanded beyond the borders of the Sasanian Empire, to Transoxiana, Baluchistan, and the Caucasus. For many decades to come, this was the easternmost limit of Muslim rule.
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