Aesop

“ The Lion agreed to this, and the Fox then rejoined his companion and contrived before long to lead him by a hidden pit, which some hunter had dug as a trap for wild animals, and into which he fell. When the Lion saw that the Ass was safely caught and couldn’t get away, it was to the Fox that he first turned his attention, and he soon finished him off, and then at his leisure proceeded to feast upon the Ass.
Betray a friend, and you’ll often find you have ruined yourself. ”