Coffman Commentaries on the Bible - Genesis 21:1-7
"And Jehovah visited Sarah, as he had said, and Jehovah did unto Sarah as he had spoken. And Sarah conceived, and bare Abraham's son in his old age, at the set time of which God had spoken to him. And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac. And Abraham circumcised his son Isaac when he was eight days old, as God had commanded him. And Abraham was a hundred years old, when his son Isaac was born unto him. And Sarah said, God hath made me to... read more
E.W. Bullinger's Companion Bible Notes - Genesis 21:4
eight. The Dominical No. See App-10 . Compare Ishmael, 13th year. read more