Don’t sell the skin till you have caught the bear.
~ English Proverb
Meaning:
Don’t count on what you haven’t got yet. Act wisely and don’t be over-optimistic.
Origin:
The origin of this saying is to be found in a fable added by Lorenzo Astemio (Laurentius Abstemius) to a collection of Aesop’s fables compiled in the 1490s.