Genesis 21:2-4 Gen. 21:2-4
2 For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him. 3 And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac. 4 And Abraham circumcised his son Isaac being eight days old, as God had commanded him.
Acts 7:8 Acts 7:8
And he gave him the covenant of circumcision: and so Abraham begat Isaac, and circumcised him the eighth day; and Isaac begat Jacob; and Jacob begat the twelve patriarchs.
(Relation)