After these things the word of the Lord came to Abram in a vision: “Fear not, Abram, I am your shield; your reward shall be very great.”
But Abram said, “O Lord God, what will you give me, for I continue childless, and the heir of my house is Eliezer of Damascus?”
And Abram said, “Behold, you have given me no offspring, and a member of my household will be my heir.”
And behold, the word of the Lord came to him: “This man shall not be your heir; your very own son shall be your heir.”
And he brought him outside and said, “Look toward heaven, and number the stars, if you are able to number them.” Then he said to him, “So shall your offspring be.”
And he believed the Lord, and he counted it to him as righteousness.
-Genesis 15:1-6 (ESV)