Article 1, Section 3, Clause 3

No Person shall be a Senator who shall not have attained to the Age of thirty Years, and been nine Years a Citizen of the United States, and who shall not, when elected, be an Inhabitant of that State for which he shall be chosen.

1.Records of the Federal Convention
2.Joseph Story, Commentaries on the Constitution 2:§§ 726--30, 1833