Genesis 21:4
And Abraham circumcised his son Isaac when he was eight days old, as God had commanded him.
Jeremiah 4:4
Circumcise yourselves to the Lord; remove the foreskin of your hearts, O men of Judah and inhabitants of Jerusalem; lest my wrath go forth like fire, and burn with none to quench it, because of the evil of your deeds.”
Romans 2:25-29
For circumcision indeed is of value if you obey the law, but if you break the law, your circumcision becomes uncircumcision. So, if a man who is uncircumcised keeps the precepts of the law, will not his uncircumcision be regarded as circumcision? Then he who is physically uncircumcised but keeps the law will condemn you who have the written code and circumcision but break the law. For no one is a Jew who is merely one outwardly, nor is circumcision outward and physical. But a Jew is one inwardly, and circumcision is a matter of the heart, by the Spirit, not by the letter. His praise is not from man but from God.