I have studied it, and I can prove its truth as clearly as any proposition ever submitted to the mind of man.

John Church Hamilton, History of the republic of the United States of America: as traced in the writings of Alexander Hamilton and of his cotemporaries, v. 7 p. 790. John Church Hamilton was Alexander Hamilton's son. He gives his source for the first quotation as the Reminiscences of General Morton, but gives no source for the second.