Genesis 17:21-25

But I will establish My covenant with Isaac, whom Sarah will bear to you at this season next year.”

When He finished talking with him, God went up from Abraham.

Then Abraham took his son Ishmael, and all the slaves who were born in his house and all who were bought with his money, every male among the men of Abraham’s household, and circumcised the flesh of their foreskin on this very same day, as God had said to him.

Now Abraham was ninety-nine years old when he was circumcised in the flesh of his foreskin.

And his son Ishmael was thirteen years old when he was circumcised in the flesh of his foreskin.