… is from Thomas Jefferson’s 1791 reflections on the U.S. Constitution’s delegation of powers to the national government. Jefferson’s quotation appears in the following passage from page 165 of Noble Cunningham’s outstanding 1987 biography of Jefferson, In Pursuit of Reason  (emphasis original to Jefferson; footnote added):
He [Jefferson] then considered the general phrase of the Constitution that identified the purpose of the taxing power as “to pay the Debts and provide for the common Defence and general Welfare of the United States.”* Congress, he said, was to levy taxes only for these purposes, not for any purpose they pleased. “In like manner they are not to do anything they please to provide for the general welfare, but only to lay taxes for that purpose.” To interpret this provision in any other way would reduce the Constitution to “a single phrase, that of instituting a Congress with power to do whatever would be for the good of the U.S. and as they would be the sole judges of good or evil, it would also be a power to do whatever evil they pleased.”
* This is Section 1, Article 8 ‘s general-welfare clause. It, along with Art. 1, Sec. 8’s “necessary and proper” clause, is misinterpreted routinely by “Progressives” (and others seeking Constitutional justification for unconstitutional expansions of national-government power) as a broad grant of permission from the Constitution’s framers to the Congress for the latter to do pretty much whatever that assembly’s members assure the public and the courts they feel is necessary and proper to promote Americans’ general welfare.