U.S. Constitution, Article I — The Legislative Branch, Section 3, Clause 5
The Senate shall chuse their other Officers, and also a President pro tempore, in the Absence of the Vice President, or when he shall exercise the Office of President of the United States.
Notes
Allows the Senate to choose its own officers, and requires it to choose a President pro tempore to preside when the Vice President is absent or is exercising the office of President of the United States. The choice of these officers rests with the Senate alone.
Use as reference
Lexinter.net | U.S. Const. art. I, § 3, cl. 5 | https://laws.lexinter.net/constitution/us/article-1/section-3/clause-5