Galatians 4:22-26
4:22 For it is written that Abraham had two sons, one by the slave woman and the other by the free woman.
4:23 But 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.
4:24 These 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.
4:25 Now Hagar represents Mount Sinai in Arabia and corresponds to the present Jerusalem, for she is in slavery with her children.
4:26 But the Jerusalem above is free, and she is our mother.