“Yes, but when I discovered it, it stayed discovered.”
On being told that a piece of work he thought was his discovery had duplicated an earlier mathematician's work. Quoted in "Pity the Scientist Who Discovers the Discovered" http://www.nytimes.com/2006/02/05/weekinreview/05kolata.html by Gina Kolata, New York Times: Week in Review (2006-02-05)