Galatians 4:22
For it is written that Abraham had two sons; one of the maid servant, and one of the free woman.
Genesis 16:15
And Hagar bore Abram a son; and Abram called the name of his son whom Hagar bore, Ishmael.
Genesis 16:2-4
And Sarai said to Abram, Behold now, Jehovah has shut me up, that I do not bear. Go in, I pray thee, to my maidservant: it may be that I shall be built up by her. And Abram hearkened 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 handmaid and her son; for the son of this handmaid shall not inherit with my son with Isaac.