Galatians 4:22
For it has been written, that Abraham had two sons, one by the bondmaid, and one by the free.
Genesis 16:15
And Hagar brought forth a son to Abram, and Abram shall call his name which Hagar brought forth, Ishmael.
Genesis 16:2-4
And Sarai will say to Abram, Behold now, Jehovah restrained me from bringing forth; go now to my maid servant; perhaps I shall have children from her. And Abram will listen to the voice of Sarai.
Genesis 21:1-2
And Jehovah reviewed Sarah as he said; and Jehovah will do to Sarah as he spake.
Genesis 21:10
And she will say to Abraham, Cast out this maid-servant and her son; for the son of this maid-servant shall not inherit with my son, with Isaak.