Third Annual Message to Congress, 7 Dec. 1903. "No one is above the law" appears in the U.S. Supreme Court case Mississippi v. Johnson (1867) (arguments of counsel). Even earlier, "no officer ... is above the law" is found in a Kentucky Supreme Court case, Johnston v. Commonwealth (1809).
Alexander Hamilton, John Church Hamilton (1850). “The Works of Alexander Hamilton: Miscellanies, 1774-1789: A full vindication; The farmer refuted; Quebec bill; Resolutions in Congress; Letters from Phocion; New-York Legislature, etc”, p.43