Genesis 17:9-13

God said further to Abraham, “Now as for you, you shall keep My covenant, you and your descendants after you throughout their generations.

This is My covenant, which you shall keep, between Me and you and your descendants after you: every male among you shall be circumcised.

And you shall be circumcised in the flesh of your foreskin, and it shall be the sign of the covenant between Me and you.

And every male among you who is eight days old shall be circumcised throughout your generations, including a slave who is born in the house or who is bought with money from any foreigner, who is not of your descendants.

A slave who is born in your house or who is bought with your money shall certainly be circumcised; so My covenant shall be in your flesh as an everlasting covenant.