Aesop's Fables (1884)
175. The Ass in the Lion's Skin.
An Ass, having put on the Lion's skin, roamed about in the forest, and amused himself by frightening all the foolish animals he met with in his wanderings. At last, meeting a Fox, he tried to frighten him also, but the Fox no sooner heard the sound of his voice, than he exclaimed: "I might possibly have been frightened myself, if I had not heard your bray."
No disguise will hide one's true character.
Aesop's Fables: A New Revised Version From Original Sources (translator not identified), 1884 . Illustrations by Ernest Henry Griset (1844-1907), John Tenniel (1820-1914) and Harrison Weir (1824-1906). Available online at Project Gutenberg.