Genesis 15:2-5

15:2 But Abram said, “O sovereign Lord, what will you give me since I continue to be childless, and my heir is Eliezer of Damascus?” 15:3 Abram added, “Since you have not given me a descendant, then look, one born in my house will be my heir!”

15:4 But look, the word of the Lord came to him: “This man will not be your heir, but instead a son who comes from your own body will be your heir.” 15:5 The Lord took him outside and said, “Gaze into the sky and count the stars – if you are able to count them!” Then he said to him, “So will your descendants be.”

Genesis 16:2

16:2 So Sarai said to Abram, “Since the Lord has prevented me from having children, have sexual relations with my servant. Perhaps I can have a family by her.” Abram did what Sarai told him.

Genesis 17:16-19

17:16 I will bless her and will give you a son through her. I will bless her and she will become a mother of nations. Kings of countries will come from her!”

17:17 Then Abraham bowed down with his face to the ground and laughed as he said to himself, “Can a son be born to a man who is a hundred years old? Can Sarah bear a child at the age of ninety?” 17:18 Abraham said to God, “O that Ishmael might live before you!”

17:19 God said, “No, Sarah your wife is going to bear you a son, and you will name him Isaac. I will confirm my covenant with him as a perpetual covenant for his descendants after him.