Le Livre de l’Impot Foncier. [Kitab al-Kharadj.]

In Islamic law, kharaj is a tax on agricultural land. Kharaj has no basis in the Qur'an or hadith, being rather the product of ijma, consensus of Islamic scholars, and urf, Islamic tradition.
Initially, after the first Muslim conquests in the 7th century, kharaj usually denoted a lump-sum duty levied upon the conquered provinces and collected by the officials of the former Byzantine and Sassanid empires or, more broadly, any kind of tax levied by Muslim conquerors on their non-Muslim subjects, dhimmis. At that time, kharaj was synonymous with jizyah, which later emerged as a poll tax paid by dhimmis. Muslims landowners, on the other hand, paid only ushr, a religious tithe, which carried a much lower rate of taxation.