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).
Benjamin Disraeli, Edmund Gosse, Robert Arnot (1904). “The Works of Benjamin Disraeli, Earl of Beaconsfield, Embracing Novels, Romances, Plays, Poems, Biography, Short Stories and Great Speeches: Contarini Fleming, v. 2. Count Alarcos. Popanilla”