Aesop's Fables
#178 The Lion and the Eagle
An Eagle stayed his flight and entreated a Lion to make an alliance with him to their mutual advantage.
The Lion replied, "I have no objection, but you must excuse me for requiring you to find surety for your good faith, for how can I trust anyone as a friend who is able to fly away from his bargain whenever he pleases?"
MORAL: Try before you trust.