TSK · Genesis 21:4

This is my covenant, which you shall keep, between me and you and your seed after you. Every male among you shall be circumcised.

When a stranger shall live as a foreigner with you, and will keep the Passover to Yahweh, let all his males be circumcised, and then let him come near and keep it; and he shall be as one who is born in the land: but no uncircumcised person shall eat of it.

Whatever thing I command you, that you shall observe to do: you shall not add thereto, nor diminish from it.

It happened on the eighth day, that they came to circumcise the child; and they would have called him Zacharias, after the name of the father.

Moses has given you circumcision (not that it is of Moses, but of the fathers), and on the Sabbath you circumcise a boy.