"Render unto Caesar..".
This, as we know, comes from the gospels. You will search in vain for any equivalent statement in the Koran, just as you will search in vain for anything like the beatitudes, "Turn the other cheek", "let him who is without sin cast the first stone" and the like.
There is a fundamental philosophical difference between Christianity, founded at the time of the Roman empire (of which Judaea was a part), and Islam which was founded in the anarchic tribal societies of 7th century Arabia. Thus Christianity has always recognised the legitimacy of secular authority (Romans 13: "Let every soul be subject unto the higher power...". Islam, on the other hand, has never theoretically recognised the legitimacy of secular rule: legitimacy derives from submission to the will of Allah, hence the Muslim Brotherhood etc. That is why fundamentalists here will say quite openly that democracy is an un-Islamic concept, and why even in the most secular Muslim majority countries like Turkey there are tensions between secularists and those who want Sharia.