Galatians 4:24
This set of circumstances contains an illustration; for these two women [Hagar and Sarah] represent the two Agreements [between God and mankind]. The one [Agreement], given at Mount Sinai, represents Hagar, whose children became [the Israelites], enslaved under bondage [to the requirements of the law of Moses].
Luke 1:7
But they had no children, because Elizabeth was unable to bear offspring due to their both being very old.
Luke 1:36
And consider this, your relative Elizabeth is also pregnant with a son in spite of her old age, and [even though] she was said to be unable to have children, she is now six months along.