Abram believed the LORD, and it was credited to him as righteousness. — Genesis 15:6

Abraham believed the Lord, and it was counted to him as righteousness. No wonder Paul jumps on this — it's the clearest example of justification by faith in the Old Testament. Abraham didn't waver in unbelief but grew strong in faith, giving glory to God. The promise didn't come through the law but through the righteousness of faith. The righteous shall live by faith.