A related question is this thread, where the subject in question were banks, and how they operated and profited under Islamic rule.
In Islamic jurisprudence (fiqh), charging interest on loans is considered usury and is illegal. How did Islamic states fund their armies to wage war? Was it all plunder as you conquer or did the states take foreign loans and adhere to the interest?
I am looking for a broad range of how different Islamic empires operated their war finances, and maybe how it evolved over time. Basically everything from the inception of Islam to the collapse of the Ottoman Empire.