Acts 7:8

“This is My covenant, which you shall keep, between Me and you and your seed after you: every male among you shall be circumcised.

“And you shall be circumcised in the flesh of your foreskin, and it shall be the sign of the covenant between Me and you.

So Sarah conceived and bore a son to Abraham in his old age, at the appointed time of which God had spoken to him.

Then Abraham circumcised his son Isaac when he was eight days old, as God had commanded him.

“For this reason Moses has given you circumcision (not because it is from Moses, but from the fathers), and on the Sabbath you circumcise a man.

“Men, brothers, I may confidently say to you regarding the patriarch David that he both died and was buried, and his tomb is with us to this day.

Now observe how great this man was to whom Abraham, the patriarch, gave a tenth of the spoils.