Genesis 15:3-6 NIV
And Abram said, “You have given me no children; so a servant in my household will be my heir.”
Then the word of the LORD came to him: “This man will not be your heir, but a son who is your own flesh and blood will be your heir.” He took him outside and said, “Look up at the sky and count the stars—if indeed you can count them.” Then he said to him, “So shall your offspring be.”
Abram believed the LORD, and he credited it to him as righteousness.
NIV: New International Version