Source, in full
When asked if he was willing to die for his beliefs. As cited by Leonard Lyons on June 23, 1964. (New York Post, Section: Post Daily Magazine, The Lyons Den by Leonard Lyons, Quote Page 27 (Magazine Page 3), Column 3, New York.) Quoted in The Times Book of Quotations (2000), p. 84.
Notes from Wikiquote
Paraphrased as "I would never die for my beliefs because I might be wrong" in The Fifth and Far Finer than the First Four 637 Best Things Anybody Ever Said, by Robert Byrne (Fawcett Columbine, 1993), 258.