Genesis 17:19-27

But God said, “No, Sarah your wife shall bear you a son indeed, and you shall name him Isaac (laughter); and I will establish My covenant with him for an everlasting covenant and with his descendants after him. As for Ishmael, I have heard and listened to you; behold, I will bless him, and will make him fruitful and will greatly multiply him [through his descendants]. He will be the father of twelve princes (chieftains, sheiks), and I will make him a great nation. [Gen 25:12-18] But My covenant [My promise, My solemn pledge], I will establish with Isaac, whom Sarah will bear to you at this time next year.” And God finished speaking with him and went up from Abraham. Then Abraham took Ishmael his son, and all the servants who were born in his house and all who were purchased with his money, every male among the men of Abraham’s household, and circumcised the flesh of their foreskin the very same day, as God had said to him. So Abraham was ninety-nine years old when he was circumcised. And Ishmael his son was thirteen years old when he was circumcised. On the very same day Abraham was circumcised, as well as Ishmael his son. All the men [servants] of his household, both those born in the house and those purchased with money from a foreigner, were circumcised along with him [as the sign of God’s covenant with Abraham].