Article 1, Section 9, Clause 2

Document 11
Thomas Jefferson to James Madison
31 July 1788(See vol. 1 , ch. 14 , no. 46 )

The Founders' Constitution
Volume 3, Article 1, Section 9, Clause 2, Document 11
http://press-pubs.uchicago.edu/founders/documents/a1_9_2s11.html
The University of Chicago Press