Article 6, Clause 2
Document 11
James Madison to Thomas Jefferson
24 Oct. 1787(See vol. 1 , ch. 17 , no. 22 )
The Founders' Constitution
Volume 4, Article 6, Clause 2, Document 11
http://press-pubs.uchicago.edu/founders/documents/a6_2s11.html
The University of Chicago Press