Rom 4:11-12

11He received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised. The purpose was to make him the ancestor of all who believe without being circumcised and who thus have righteousness reckoned to them,12and likewise the ancestor of the circumcised who are not only circumcised but who also follow the example of the faith that our ancestor Abraham had before he was circumcised.