Galatians 4:22
For it is written: Abraham had two sons, the one out of the slave-woman, and one out of the free woman.
Genesis 16:15
And Hagar bore Abram a son. And Abram called his son's name, which Hagar bore, Ishmael.
Genesis 16:2-4
And Sarai said to Abram, Behold now, Jehovah has kept me from bearing. I pray you, go in to my slave woman. It may be that I may be built by her. And Abram listened to the voice of Sarai.
Genesis 21:1-2
And Jehovah visited Sarah as He had said. And Jehovah did to Sarah as He had spoken.
Genesis 21:10
And she said to Abraham, Cast out this slave woman and her son. For the son of this slave woman shall not be heir with my son, with Isaac.