Article 1, Section 9, Clause 3
Oliver Ellsworth, Landholder, no. 610 Dec. 1787Essays 163
There is to be no ex post facto laws. This was moved by Mr. Gerry and supported by Mr. Mason, and is exceptional only as being unnecessary; for it ought not to be presumed that government will be so tyrannical, and opposed to the sense of all modern civilians, as to pass such laws: if they should, they would be void.
The Founders' Constitution
Volume 3, Article 1, Section 9, Clause 3, Document 9
The University of Chicago Press
Ford, Paul Leicester, ed. Essays on the Constitution of the United States, Published during Its Discussion by the People, 1787--1788. Brooklyn: Historical Printing Club, 1892.
Easy to print version.