Genesis 17:10-13

This is [the sign of] My covenant, which you shall keep and faithfully obey, 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 foreskins, and it shall be the sign (symbol, memorial) of the covenant between Me and you. Every male among you who is eight days old shall be circumcised throughout your generations, [including] a servant whether born in the house or one who is purchased with [your] money from any foreigner, who is not of your descendants. A servant who is born in your house or one who is purchased with your money must be circumcised; and [the sign of] My covenant shall be in your flesh for an everlasting covenant.