In Lekh Lekha we read:
After these things the word of the Lord came to Avram in a vision, saying, Fear not, Avram; I am your shield, and your reward will be great.
And Avram said, Lord God, what will you give me,

seeing I go childless, and the steward of my house is that Eliezer of Damascus?
And Avram said, Behold, to me you have given no seed; and, lo, one born in my house is my heir (

Original post by Ben Rambam