Non-Muslims who converted to Islam were required to continue to pay the same jizya tax they had paid before their conversion. In theory, this would protect the Ummayad caliphate from losing a valuable tax base, and ensure that all conversions would be sincere. In practice, it meant institutionalised discrimination based on race. Since the Arabs had almost entirely converted to Islam before the Ummayad caliphate began, the only people who were converting into the religion were non-Arabs such as Copts, Greeks, Berbers, and especially Persians. They were the only Muslims paying jizya, while their Arab brothers in faith were exempt. The intention of the Ummayads may have been to protect their tax base, but the policy ended up having a racial aspect, keeping non-Arabs at the bottom of society while Arabs rose to the top. From a religious perspective, this directly contradicted Prophet Muhammad's call for unity during the Farewell Pilgrimage, when he famously proclaimed, "No Arab is better than a non-Arab and no non-Arab is better than an Arab".
An attempt was made by the caliph Umar ibn al Abd al Aziz to undo the un-Islamic taxation policy during his reign from 717 to 720. Although his reforms were widly popular with the non-Arabs of the empire, he was distrusted by his own family for his views on equality and was poisoned by the Ummayad clan just two years after taking power.