So Sarah conceived and bore a son to Abraham in his old age, at the very time God had promised.

Acts 7:8
Then God gave Abraham the covenant of circumcision, and Abraham became the father of Isaac and circumcised him on the eighth day. And Isaac became the father of Jacob, and Jacob of the twelve patriarchs.

Galatians 4:22
For it is written that Abraham had two sons, one by the slave woman and the other by the free woman.

Hebrews 11:11
By faith Sarah, even though she was barren and beyond the proper age, was enabled to conceive a child, because she considered Him faithful who had promised.

Genesis 17:19
But God replied, "Your wife Sarah will indeed bear you a son, and you are to name him Isaac. I will establish My covenant with him as an everlasting covenant for his descendants after him.

Genesis 17:21
But I will establish My covenant with Isaac, whom Sarah will bear to you at this time next year."

Genesis 18:10
Then the LORD said, "I will surely return to you at this time next year, and your wife Sarah will have a son!" Now Sarah was behind him, listening at the entrance to the tent.

Genesis 18:14
Is anything too difficult for the LORD? At the appointed time I will return to you--in about a year--and Sarah will have a son."

For Sarah conceived, and bore Abraham a son in his old age, at the set time of which God had spoken to him.