[Gen 17:16 KJV] 16 And I will bless her, and give thee a son also of her: yea, I will bless her, and she shall be [a mother] of nations; kings of people shall be of her.
[Gen 18:10 KJV] 10 And he said, I will certainly return unto thee according to the time of life; and, lo, Sarah thy wife shall have a son. And Sarah heard [it] in the tent door, which [was] behind him.
[Gen 21:1-3 KJV] 1 And the LORD visited Sarah as he had said, and the LORD did unto Sarah as he had spoken. 2 For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him. 3 And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac.