Genesis 17:15-19

17:15 Then God said to Abraham, “As for your wife, you must no longer call her Sarai; Sarah will be her name. 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.

Genesis 18:10-14

18:10 One of them said, “I will surely return to you when the season comes round again, and your wife Sarah will have a son!” (Now Sarah was listening at the entrance to the tent, not far behind him. 18:11 Abraham and Sarah were old and advancing in years; Sarah had long since passed menopause.) 18:12 So Sarah laughed to herself, thinking, “After I am worn out will I have pleasure, especially when my husband is old too?”

18:13 The Lord said to Abraham, “Why did Sarah laugh and say, ‘Will I really have a child when I am old?’ 18:14 Is anything impossible for the Lord? I will return to you when the season comes round again and Sarah will have a son.”

Genesis 21:1-2

The Birth of Isaac

21:1 The Lord visited Sarah just as he had said he would and did for Sarah what he had promised. 21:2 So Sarah became pregnant and bore Abraham a son in his old age at the appointed time that God had told him.

Romans 4:18-21

4:18 Against hope Abraham believed in hope with the result that he became the father of many nations according to the pronouncement, “so will your descendants be.” 4:19 Without being weak in faith, he considered his own body as dead (because he was about one hundred years old) and the deadness of Sarah’s womb. 4:20 He did not waver in unbelief about the promise of God but was strengthened in faith, giving glory to God. 4:21 He was fully convinced that what God promised he was also able to do.

Romans 10:8

10:8 But what does it say? “The word is near you, in your mouth and in your heart” (that is, the word of faith that we preach),

Hebrews 11:11

11:11 By faith, even though Sarah herself was barren and he was too old, he received the ability to procreate, because he regarded the one who had given the promise to be trustworthy.