Article 1, Section 9, Clause 5

No Tax or Duty shall be laid on Articles exported from any State.

1.Records of the Federal Convention
2.James Madison to Thomas Jefferson, 24 Oct. 1787
3.James McHenry, Maryland House of Delegates, 29 Nov. 1787
4.Joseph Story, Commentaries on the Constitution 2:§§ 1011--12, 1833