Mass conversion to Islam forced the treasury to tie tax to land, not religion.

Evidence

As a result of the acquisition of land outside Arabia by Arab Muslims on the one hand, and of the conversion of non-Arab landowners to Islam on the other hand, the treasury suffered a serious loss of revenue, and the transformation of khara¯j-land into tithe-land was therefore stopped. Thereafter by a legal fiction the tax was deemed to be due from the land and not from the landowner, and all khara¯j-land paid khara¯j, irrespective of any changes in the religion of the owner or cultivator. The only remaining fiscal privilege of the Muslim was that he was exempt from the jizya, the polltax paid by all non-Muslims. — Bernard Lewis, From Babel to Dragomans, 352 (#corroborates, via linked claim)

Categorization

• XREF: connects to: Mass conversion threatened state revenue, prompting a legal fiction taxing the land itself — Bernard Lewis, From Babel to Dragomans: Interpreting…, 352; Forced baptism enlarged the Church’s tax base by converting non-payers into tithe-payers — L. P. Harvey, Muslims in Spain, 1500 to 1614, 253

Broader Connections

• Mass conversion threatened state revenue, prompting a legal fiction taxing the land itself #corroborates (0.95) — Bernard Lewis, From Babel to Dragomans, 352