He thus explicitly stated that the kharaj is lifted from land acquired through a settlement when its inhabitants embrace Islam. This is understood to mean that those lands belong to them. It is not lifted from land taken by force, because that land belongs to the Muslims collectively, and the kharaj is rent owed for it.
As for the amount of kharaj imposed, it is determined according to what the land can bear. Ahmad stated this in the report of Muḥammad ibn Dāwūd. He was asked about ʿUmar’s report: “He imposed such-and-such on a jریب of vines, and such-and-such on a jریب of another crop.” Is this a fixed assessment imposed on the people, not to be increased, or may the imam increase or decrease it if he deems otherwise? He replied: “Rather, it is according to the imam’s judgment: if he wishes, he may increase it, and if he wishes, he may decrease it.” He then said: “This is clear in ʿUmar’s report: ‘If you increase such-and-such upon them, it will not overburden them.’ ʿUmar only considered what the land could bear.”
He thus explicitly stated that the matter is left to the imam’s independent legal reasoning and is not restricted to ʿUmar’s assessment. Rather, the land’s capacity is to be taken into consideration when increasing or decreasing the kharaj. He cited ʿUmar’s statement: “If you increase it for them, do not overburden them.”
Al-ʿAbbās ibn Muḥammad ibn Mūsā al-Khallāl transmitted from Ahmad that he said: “The kharaj may remain in their hands as a crop share of one-half, or less if the cultivators agree to it; they are to be charged only according to what they can bear.” He subsequently said: “The imam may not alter it from the arrangement established by ʿUmar.”
In the report of Yaʿqūb ibn Bukhtān, he said: “It is not permissible for the imam to decrease it, but he may increase it.” In the report of Ibn Manṣūr, he said: “He”—meaning ʿUmar—“imposed kharaj upon it”—meaning the Sawād—“at the rate of one dirham and one qafīz of wheat or barley for every jریب. As for crops other than these, such as reeds, olive trees, and date palms…”