Galatians 4:22

For it is written that Abraham had two sons, one by the slave woman [Hagar] and one by the free woman [Sarah].

Genesis 16:15

So Hagar gave birth to Abram’s son; and Abram named his son, to whom Hagar gave birth, Ishmael (God hears).

Genesis 16:2-4

So Sarai said to Abram, “See here, the Lord has prevented me from bearing children. I am asking you to go in to [the bed of] my maid [so that she may bear you a child]; perhaps I will obtain children by her.” And Abram listened to Sarai and did as she said.

Genesis 21:1-2

The Lord graciously remembered and visited Sarah as He had said, and the Lord did for her as He had promised.

Genesis 21:10

Therefore she said to Abraham, “Drive out this maid and her son, for the son of this maid shall not be an heir with my son Isaac.”

Treasury of Scripture Knowledge

Summary

For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman.

Bible References

That

Genesis 16:2
So Sarai said to Abram, “See here, the Lord has prevented me from bearing children. I am asking you to go in to [the bed of] my maid [so that she may bear you a child]; perhaps I will obtain children by her.” And Abram listened to Sarai and did as she said.
Genesis 21:1
The Lord graciously remembered and visited Sarah as He had said, and the Lord did for her as He had promised.