Galatians 4:22-25

22For it is written that Abraham had two sons, one by the slave woman and the other by the free woman.

23But one, the son by the slave woman, was born by natural descent, while the other, the son by the free woman, was born through the promise.

24These things may be treated as an allegory, for these women represent two covenants. One is from Mount Sinai bearing children for slavery; this is Hagar.

25Now Hagar represents Mount Sinai in Arabia and corresponds to the present Jerusalem, for she is in slavery with her children.