Romans 9:8-10

New International Version - UK

⁸ In other words, it is not the children by physical descent who are God’s children, but it is the children of the promise who are regarded as Abraham’s offspring. ⁹ For this was how the promise was stated: ‘At the appointed time I will return, and Sarah will have a son.’^[a]

¹⁰ Not only that, but Rebekah’s children were conceived at the same time by our father Isaac.