2 U.S. Code § 25 - Oath of Speaker, Members, and Delegates
At the first session of Congress after every general election of Representatives, the oath of office shall be administered by any Member of the House of Representatives to the Speaker; and by the Speaker to all the Members and Delegates present, and to the Clerk, previous to entering on any other business; and to the Members and Delegates who afterward appear, previous to their taking their seats.
The Clerk of the House of Representatives of the Eightieth and each succeeding Congress shall cause the oath of office to be printed, furnishing two copies to each Member and Delegate who has taken the oath of office in accordance with law, which shall be subscribed in person by the Member or Delegate, who shall thereupon deliver them to the Clerk, one to be filed in the records of the House of Representatives, and the other to be recorded in the Journal of the House and in the Congressional Record; and such signed copies, or certified copies thereof, or of either of such records thereof, shall be admissible in evidence in any court of the United States, and shall be held conclusive proof of the fact that the signer duly took the oath of office in accordance with law.
R.S. § 30 derived from act June 1, 1789, ch. 1, § 2, 1 Stat. 23.
The last paragraph of this section, which permitted Members and Delegates of the House of Representatives of the Eightieth Congress to subscribe and deliver two signed copies of the printed oath of office at any time before the expiration of the Eightieth Congress, was omitted.
1948—Act Feb. 18, 1948, added last two paragraphs to provide a way by which any Member of House of Representatives can establish by record evidence the fact that the Member took the oath of office and so became a Member.