Vernon Jones (1912)
65. THE QUACK FROG
Once upon a time a Frog came forth from his home in the marshes and proclaimed to all the world that he was a learned physician, skilled in drugs and able to cure all diseases. Among the crowd was a Fox, who called out, "You a doctor! Why, how can you set up to heal others when you cannot even cure your own lame legs and blotched and wrinkled skin?"
Physician, heal thyself.
Aesop's Fables: A New Translation by V.S. Vernon Jones with illustrations by Arthur Rackham (1912). This book is available online at Project Gutenberg.