2 USC § 191. Oaths to witnesses
The President of the Senate, the Speaker of the House of Representatives, or a chairman of any joint committee established by a joint or concurrent resolution of the two Houses of Congress, or of a committee of the whole, or of any committee of either House of Congress, is empowered to administer oaths to witnesses in any case under their examination.
Any member of either House of Congress may administer oaths to witnesses in any matter depending in either House of Congress of which he is a Member, or any committee thereof.
(R.S. §101; June 26, 1884, ch. 123, 23 Stat. 60; June 22, 1938, ch. 594, 52 Stat. 942, 943.)