From Aesop's Fables :The Wolf in Sheep's Clothing

A wolf decided to disguise himself in order that he might prey upon a flock of sheep without fear of finding out by the shepherd. So he clothed himself in a sheepskin and slipped among the sheep when they were out at pasture. The shepherd completely did not notice him. When the flock was fenced in for the night he was shut in with the rest of the sheep. But it happened that very night the shepherd required a supply of mutton for the table, laid hands on the wolf in mistake for a sheep and killed him with his knife on the spot.