"There is only one difference between a madman and me. I am not mad."
— Salvador Dalí, as quoted in:
(1956, July).
Dalí is a dilly.
The American Magazine, 162(1),
28–9, 107–9.
There have been a few magazines known as The American or some variant; this one is the one published by the Crowell-Collier Publishing Company of Springfield, Ohio, from 1906 to 1956. (In fact the July 1956 issue was the second-last.) The quote itself is split across pages 28 and 107, and presented thus:
"There ees only wan deefer-ance between a madman and me," he [Dalí] tells you. "I am not mad." And adds: "There is more to ze nightmarish world than people theenk."
Scans of the relevant pages: