Article 1, Section 6, Clause 1
Bill of Rights, sec. 91 W. & M., 2d sess., c. 2 , 16 Dec. 1689
9. That the freedom of speech, and debates or proceedings in parliament, ought not to be impeached or questioned in any court or place out of parliament.
The Founders' Constitution
Volume 2, Article 1, Section 6, Clause 1, Document 1
The University of Chicago Press
Easy to print version.