I am deeply sensible of the honor done me by the American people in thus expressing their confidence in what I have done and have tried to do. I appreciate in the full the solemn responsibility this confidence imposes upon me, and I shall do all that in my power lies not to forfeit it. On the Fourth of March next I shall have served three and one-half years, and this three and one-half years constitutes my first term. The wise custom which limits the President to two terms regards the substance and not the form. Under no circumstances will I be a candidate for or accept another nomination.
Source: "Roosevelt Sweeps North and West and Is Elected President. Says He Will Not Run Again," New York Times, November 9, 1904, p. 1.
Theodore Roosevelt, Statement Following Victory in the Presidential Election Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/345951