|The Samuel Johnson Sound Bite Page -> Apocrypha -> Your manuscript is both good and original. But the part that is good is not original, and the part that is original is not good.|
Samuel Johnson did not say:
Many people believe Samuel Johnson said it, but no one seems to have found it anywhere in his works or letters, or, for that matter any of the biographies of him by his contemporaries.
I'm basing that on what's been included in Primary Source Media's CD-ROM of Johnson and Boswell. The CD-ROM includes all of Johnson's writings in the canon, Boswell's Life of Johnson and Tour of the Hebrides, as well as accounts from Hester Thrale, Sir John Hawkins, Fanny Burney, plus O.M. Brack's "Early Biographies." In short, practically nothing from the 18th Century has been left out. In addition, I've also consulted "The Beauties of Johnson," an 18th Century collection of Johnson quotations.
Simply put, as amusing as the quip is, it hasn't been found anywhere. Until someone can find a source for it, you're best off saying it's "attributed, not found."