[AdmSmith]

If you became a convert, your taxes were immediately eliminated, as was your tithe. If you didn’t, you faced death.

This seems to be a common strategies for changing religion. In Europe the early spread of Christianity was encouraged by the taxation. You could only inherit if you were a Christian.

[Axenolith]

The big difference being that the Islamic War and Conquest Manual (Koran) puts that in print while the Bible doesn't...