Article 1, Section 4, Clause 1
Document 19
James Iredell, Proposed Amendment, North Carolina Ratifying Convention
1 Aug. 17884. The Congress shall not alter, modify, or interfere in the times, places, or manner, of holding elections for senators and representatives, or either of them, except when the legislature of any state shall neglect, refuse, or be disabled by invasion or rebellion, to prescribe the same.
The Founders' Constitution
Volume 2, Article 1, Section 4, Clause 1, Document 19
http://press-pubs.uchicago.edu/founders/documents/a1_4_1s19.html
The University of Chicago Press
Elliot, Jonathan, ed. The Debates in the Several State Conventions on the Adoption of the Federal Constitution as Recommended by the General Convention at Philadelphia in 1787. . . . 5 vols. 2d ed. 1888. Reprint. New York: Burt Franklin, n.d.