Galatians 4:22
For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman.
Genesis 16:15
And Hagar bare Abram a son: and Abram called his son's name, which Hagar bare, Ishmael.
Genesis 16:2-4
And Sarai said unto Abram, Behold now, the LORD hath restrained me from bearing: I pray thee, go in unto my maid; it may be that I may obtain children by her. And Abram hearkened to the voice of Sarai.
Genesis 21:1-2
And the LORD visited Sarah as he had said, and the LORD did unto Sarah as he had spoken.
Genesis 21:10
Wherefore she said unto Abraham, Cast out this bondwoman and her son: for the son of this bondwoman shall not be heir with my son, even with Isaac.