The Library of Congress website has the following transcript of a June 20, 1803 letter from President Thomas Jefferson to his private secretary, Capt. Meriwether Lewis:

“Your situation as Secretary of the President of the U. S. has made you acquainted with the objects of my confidential message of Jan. 18, 1803 to the legislature; you have seen the act they passed, which, tho' expressed in general terms, was meant to sanction those objects, and you are appointed to carry them into execution.”

The “confidential message” to which Jefferson referred was his January 18 request that Congress appropriate $2,500 to fund an expedition “to explore the Missouri river; & such principal stream of it, as by it's [sic] course & communication with the waters of the Pacific ocean, may offer the most direct & practicable water communication across this continent, for the purpose of commerce.”