James Madison wrote this in 1785, in "Memorial and Remonstrance Against Religious Assessments," in which he argued against a bill meant to levy a tax in Virginia in order to pay religious teachers:

...the Bill implies either that the Civil Magistrate is a competent Judge of Religious Truth; or that he may employ Religion as an engine of Civil policy. The first is an arrogant pretension falsified by the contradictory opinions of Rulers in all ages, and throughout the world: the second an unhallowed perversion of the means of salvation.

Here's another excerpt:

...it is proper to take alarm at the first experiment on our liberties. We hold this prudent jealousy to be the first duty of Citizens, and one of the noblest characteristics of the late Revolution. The free men of America did not wait till usurped power had strengthened itself by exercise, and entangled the question in precedents. They saw all the consequences in the principle, and they avoided the consequences by denying the principle. We revere this lesson too much soon to forget it. Who does not see that the same authority which can establish Christianity, in exclusion of all other Religions, may establish with the same ease any particular sect of Christians, in exclusion of all other Sects? that the same authority which can force a citizen to contribute three pence only of his property for the support of any one establishment, may force him to conform to any other establishment in all cases whatsoever?