Galatians 4:23
But the child of the slave girl was born in the ordinary course of nature, while the child of the free woman was born to fulfill the promise.
Hebrews 11:11
By faith Sarah received strength to become pregnant, and actually gave birth to a child, although she was past the time of life for it, because she thought that He who made her the promise was to be trusted.
Romans 9:7-8
nor are they all children of Abraham, because they are his descendants, but the promise was "In the line of Isaac your descendants will I be counted."
Romans 4:18-21
Abraham, building on hope in spite of hopeless circumstances, had faith, and so he actually became the father of many nations, just as it had been told him, "So numberless shall your descendants be."
Romans 10:8
But what does it say? "God's message is close to you, on your very lips and in your heart"; that is, the message about faith which we preach.
Galatians 4:28-29
Now we, brothers, like Isaac, are children born to fulfill the promise.