Galatians 4:23
but while the son by the slave woman was born according to the flesh, the son by the free woman was born in fulfilment of a promise.
Hebrews 11:11
By faith even Sarah herself received power to conceive seed, although she was past the age for child-bearing, because she counted Him faithful who had promised;
Romans 9:7-8
they are not all children of Abraham because they are Abraham's descendants. The promise was, In Isaac shall thy posterity be called.
Romans 4:18-21
For Abraham, hoping against hope, had faith to the end that he might become a father of many nations, according to that which had been spoken, So numberless shall your descendants be.
Romans 10:8
But what does it say? The word is near thee, even in thy mouth and in thy heart. That is the very word of faith which we preach;
Galatians 4:28-29
But you, brothers, are like Isaac, children of the promise;