Luke 1:13
But the angel said to him: " Do not be afraid, Zechariah; your prayer has been heard, and your wife Elizabeth shall bear you a son, whom you shall call by the name John.
Romans 9:8-9
This means that it is not the children born in the course of nature who are God's Children, but it is the children born in fulfillment of the Promise who are to be regarded as Abraham's descendants.
Galatians 4:23
But the child of the slave-woman was born in the course of nature, while the child of the free woman was born in fulfillment of a promise.
Galatians 4:28
As for ourselves, brothers, we, like Isaac, are children born in fulfillment of a promise.