Romans 4:11-12

He received the sign of circumcision, a seal or confirmation of the righteousness which he had by faith while [he was still] uncircumcised—this was so that he would be the [spiritual] father of all who believe without being circumcised—so that righteousness would be credited to them, and [that he would be] the [spiritual] father of those circumcised who are not only circumcised, but who also walk in the steps of the faith of our father Abraham which he had before he was circumcised.