Genesis 17:12-13

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.