Genesis 15:1-6  NAS          

After these things the word of the Lord cane to Abram in a vision, saying, "Do not fear, Abram, I am a shield to you; your reward shall be very great."  Abram said, "O Lord God, what will you give me, since I am childless, and the heir of my house is Eliezer of Damascus?"  And Abram said, "Since You have given no off-spring to me, one born in my house is my heir."  Then behold, the word of the Lord came to him, saying, "This man will not be your heir; but one who will come forth from your own body, he shall be your heir."  And He took him outside and said, "Now look toward the heavens, and count the stars, if you are able to count them."  And He said to him, "So shall your descendants be."  Then he believed in the Lord; and He reckoned it to him as righteousness.