The Jews: Circumcised in Token of Their Covenant Relation
Source: TTT
Genesis 17:10, 11
This is My covenant with you and your descendants after you, which you are to keep: Every male among you must be circumcised. / You are to circumcise the flesh of your foreskin, and this will be a sign of the covenant between Me and you.
Acts 7:8
Then God gave Abraham the covenant of circumcision, and Abraham became the father of Isaac and circumcised him on the eighth day. And Isaac became the father of Jacob, and Jacob of the twelve patriarchs.