After these things the word of the LORD came unto Abram in a vision, saying,
“Fear not, Abram: I am thy shield, and thy exceeding great reward.”
And Abram said, “Lord GOD, what wilt Thou give me, seeing I go childless, and the steward of my house is this Eliezer of Damascus?’ And Abram said, ‘Behold, to me Thou hast given no seed: and, lo, one born in my house is mine heir.”   And, behold, the word of the LORD came unto him, saying,
“This shall not be thine heir; but he that shall come forth out of thine own bowels shall be thine heir.”  And He brought him forth abroad, and said, ‘Look now toward heaven, and tell the stars, if thou be able to number them:’ and he said unto him, ‘So shall thy seed be.”
And he believed in the LORD; and He counted it to him for righteousness.    Genesis 15:1-6

For further study: Romans 4:3, 18, 20-25; 9:7-8; 2 Corinthians 5:19; Galatians 3:6-14; Hebrews 11:12; James 2:23