Don't whistle before you are out of the woods proverb
Don't conclude a problem solved until it is completely resolved.
"Your heart operation was successful. You are no longer in any danger" - "There might be some complications. Don't whistle before you are out of the woods".
"The problem will be solved if he agrees to help us." - "Don't whistle before you are out of the woods".
Meaning absolutely certain or without a doubt
I am as sure as God made little green apples that Peter's the one for you, you two make a beautiful couple.