Galatians 4:22
For it is written that Abraham had two sons, one by a slave woman and the other by a free woman.
Genesis 16:15
Hagar eventually gave birth to Abram's son. Abram named his son whom Hagar bore Ishmael.
Genesis 16:2-4
So Sarai told Abram, "You are well aware that the LORD has prevented me from giving birth to a child. Go have sex with my servant, so that I may possibly bear a son through her."
Genesis 21:1-2
The LORD came to Sarah, just as he had said, and the LORD did for Sarah what he had promised.
Genesis 21:10
she told Abraham, "Throw out this slave girl, along with her son, because this slave's son will never be a co-heir with my son Isaac!"