'Eighth' in the Bible

Generation after generation, every male among you is to be circumcised on the eighth day after his birth, including the servant born in your house or the one purchased from a foreigner, who is not of your offspring.

Any uncircumcised male who does not have the foreskin of his flesh circumcised on the eighth day after his birth is to be eliminated from his people because he has broken my covenant."

On the eighth day after his son Isaac had been born, Abraham circumcised him, just as God had commanded him.