The substance of this is written, Genesis 16:1-16, where we read of Abraham's having Ishmael by Hagar his bondwoman; and Genesis 21:2, where we read of the birth of Isaac, whom he had by Sarah, who was his wife.
Related Commentaries of Galatians 4:22
Galatians 4:22
22 For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman.