Galatians 3:16
Now it was to Abraham that the promises were made, 'and to his offspring.' It was not said 'to his offsprings,' as if many persons were meant, but the words were 'to thy offspring,' showing that one person was meant--and that was Christ.
Romans 9:8
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 4:28
As for ourselves, brothers, we, like Isaac, are children born in fulfillment of a promise.
Hebrews 11:13
All these died sustained by faith. They did not obtain the promised blessings, but they saw them from a distance and welcomed the sight, and they acknowledged themselves to be only aliens and strangers on the earth.