Genesis 21:4

And he circumcised him on the eighth day, just as God had instructed him

Other versions

King James Version

And Abraham circumcised his son Isaac being eight days old, as God had commanded him.

English Standard Version

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

New International Version

When his son Isaac was eight days old, Abraham circumcised him, as God commanded him.