Article 1, Section 6, Clause 2

No Senator or Representative shall, during the Time for which he was elected, be appointed to any civil Office under the Authority of the United States, which shall have been created, or the Emoluments whereof shall have been encreased during such time; and no Person holding any Office under the United States, shall be a Member of either House during his Continuance in Office.

1.Records of the Federal Convention
2.James Wilson, Pennsylvania Ratifying Convention, 4 Dec. 1787
3.Luther Martin, Genuine Information, 1788
4.Federal Farmer, no. 13, 14 Jan. 1788
5.Debate in Virginia Ratifying Convention, 14 June 1788
6.House of Representatives, Plurality of Offices, 28 Mar. 1 Apr. 1806
7.Hinds' Precedents of the House of Representatives, sec. 499, Jan. 1818
8.Senate, Select Committee Report on Amendment to Constitution, 1 Mar. 1826
9.William Wirt, Contracts with Members of Congress, 18 July 1826
10.Joseph Story, Commentaries on the Constitution 2:§§ 864--69, 1833