Genesis 21:2-5

BBE(i) 2 And Sarah became with child, and gave Abraham a son when he was old, at the time named by God. 3 And Abraham gave to his son, to whom Sarah had given birth, the name Isaac. 4 And when his son Isaac was eight days old, Abraham made him undergo circumcision, as God had said to him. 5 Now Abraham was a hundred years old when the birth of Isaac took place.