Article 6, Clause 3

Document 13

James Madison to Edmund Pendleton

Is not a religious test as far as it is necessary, or would operate, involved in the oath itself? If the person swearing believes in the supreme Being who is invoked, and in the penal consequences of offending him, either in this or a future world or both, he will be under the same restraint from perjury as if he had previously subscribed a test requiring this belief. If the person in question be an unbeliever in these points and would notwithstanding take the oath, a previous test could have no effect. He would subscribe it as he would take the oath, without any principle that could be affected by either.

The Founders' Constitution
Volume 4, Article 6, Clause 3, Document 13
http://press-pubs.uchicago.edu/founders/documents/a6_3s13.html
The University of Chicago Press

The Papers of James Madison. Edited by William T. Hutchinson et al. Chicago and London: University of Chicago Press, 1962--77 (vols. 1--10); Charlottesville: University Press of Virginia, 1977--(vols. 11--).