Article 1, Section 10, Clause 2
Document 9
Brown v. Maryland
12 Wheat. 419 1827(See 1.8.3 [commerce], no. 17 )
The Founders' Constitution
Volume 3, Article 1, Section 10, Clause 2, Document 9
http://press-pubs.uchicago.edu/founders/documents/a1_10_2s9.html
The University of Chicago Press