Acts 7:8; Romans 4:11

And xhe gave him the covenant of circumcision. And yso Abraham became the father of Isaac, and zcircumcised him on the eighth day, and aIsaac became the father of Jacob, and bJacob of the twelve patriarchs.

11 cHe received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised. The purpose was dto make him the father of all who believe without being circumcised, so that righteousness would be counted to them as well,