For circumcision verily profiteth, if thou keep the law: but if thou be a breaker of the law, thy circumcision is made uncircumcision.
Romans 2:25
This is my covenant, which ye shall keep, between me and you and thy seed after thee; Every man child among you shall be circumcised.
Genesis 17:10
And certain men which came down from Judaea taught the brethren, and said, Except ye be circumcised after the manner of Moses, ye cannot be saved.
Acts 15:1 (Leviticus 12:2-3, 6)