[1] With the first Muslim conquests in the 7th century, the kharaj initially was synonymous with jizyah and denoted a lump-sum duty levied upon the lands of conquered provinces, which was collected by hold-over officials of the defeated Byzantine Empire in the west and the Sassanid Empire in the east; later and more broadly, kharaj refers to a land-tax levied by Muslim rulers on their non-Muslim subjects, collectively known as dhimmi.
Muslim landowners, on the other hand, paid ushr, a religious tithe on land, which carried a lower rate of taxation,[2] and zakat.
Ushr was a reciprocal 10% levy on agricultural land as well as merchandise imported from states that taxed Muslims on their products.
The reforms of Umar II were finalized under the Abbasids and would thereafter form the model of tax systems in the Islamic state.
[3] From that time on, kharaj was also used as a general term describing all kinds of taxes: for example, the classic treatise on taxation by the 9th century jurist Abu Yusuf was called Kitab al-Kharaj, i.e.