And he said, I will certainly return unto thee according to the time of life; and, lo, Sarah thy wife shall have a son. And Sarah heard it in the tent door, which was behind him. I will certainly return - Abraham was now ninety-nine years of age, and this promise was fulfilled when he was a hundred; so that the phrase according to the time of life must mean either a complete year, or nine months from the present time, the ordinary time of pregnancy. Taken in this latter sense, Abraham was now in the ninety-ninth year of his age, and Isaac was born when he was in his hundredth year.
Related Commentaries of Genesis 18:10
Genesis 18:10
10 And he said, I will certainly return unto thee according to the time of life; and, lo, Sarah thy wife shall have a son. And Sarah heard it in the tent door, which was behind him.