Known sourcecanonical
"We have met the enemy, and they are ours."
Oliver H. Perry / Letter to General Harrison (dated "United States Brig Niagara. Off the Western Sisters. Sept. 10, 1813, 4 P. M.").
Letter to General Harrison (dated "United States Brig Niagara. Off the Western Sisters. Sept. 10, 1813, 4 P. M.").
Bartlett's Familiar Quotations, 9th ed. (Little, Brown, 1905), public domain