don't count your chickens before they're hatched
Definition from Wiktionary, the free dictionary
Alternative forms 
- You should not count on something before it happens.
- You should not expect all of your hopes to be fulfilled.
don't count on things if you don't have them yet
- Gregory Y. Titelman, Random House Dictionary of Popular Proverbs and Sayings, 1996, ISBN 0-679-44554-4, p. 63.