Genesis 18:10

²Sarah conceived, and bore Abraham a son in his old age, at the set time of which God had spoken to him.

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

⁸That is, it is not the children of the flesh who are children of God, but the children of the promise are counted as heirs. ⁹For this is a word of promise: “At the appointed time I will come, and Sarah will have a son.”

¹⁶He said, “At this season next year, you will embrace a son.” She said, “No, my lord, you man of God, do not lie to your servant.”

¹⁷The woman conceived, and bore a son at that season when the time came around, as Elisha had said to her.

¹⁹God said, “No, but Sarah, your wife, will bear you a son. You shall call his name Isaac.^[+] I will establish my covenant with him for an everlasting covenant for his offspring after him.

¹⁶I will bless her, and moreover I will give you a son by her. Yes, I will bless her, and she will be a mother of nations. Kings of peoples will come from her.”

¹⁵The LORD’s angel called to Abraham a second time out of the sky, ¹⁶and said, “‘I have sworn by myself,’ says the LORD, ‘because you have done this thing, and have not withheld your son, your only son,

¹⁰The LORD’s angel said to her, “I will greatly multiply your offspring, that they will not be counted for multitude.”

²⁸Now we, brothers, as Isaac was, are children of promise.

²³However, the son by the servant was born according to the flesh, but the son by the free woman was born through promise.