
“If you tell the truth you don't have to remember anything.”
Notebook entry, January or February 1894, Mark Twain's Notebook, ed. Albert Bigelow Paine (1935), p. 240 http://books.google.com/books?id=DjBVlb7cBSIC&pg=PA240
Variant: If you tell the truth you do not need a good memory!
Source: The Adventures of Huckleberry Finn