Genesis 17:21

17:21 But I will establish my covenant with Isaac, whom Sarah will bear to you at this set time next year.”

Genesis 18:10

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.

Genesis 18:14

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 21:2

21:2 So Sarah became pregnant and bore Abraham a son in his old age at the appointed time that God had told him.