Galatians 4:22
For it is written that Abraham had two sons, the one by a bondmaid, the other by a free woman.
Genesis 16:15
And Hagar bare Abram a son, and Abram called his son's name which Hagar bare, Ishmael.
Genesis 16:2-4
Wherefore she said unto Abram, "Behold the LORD hath closed me, that I can not bear. I pray thee go in unto my maid, peradventure I shall be multiplied by means of her." And Abram heard the voice of Sarai.
Genesis 21:1-2
The LORD visited Sara as he had said, and did unto her according as he had spoken.
Genesis 21:10
Then she said unto Abraham, "Put away this bondmaid and her son: for the son of this bondwoman shall not be heir with my son Isaac."