Genesis 21:5

And Abraham was an hundred years old when son Isaac was born unto him. So that this was years after his departure from Haran, and coming into the land of Canaan, for then he was seventy five years of age, Genesis 12:4 ; and this exactly agrees with the account of Demetrius, as related by Polyhistor, an Heathen writer F15 Apud Euseb. Praepar. Evangel. l. 9. c. 21. p. 425. , who makes Isaac to be born just twenty five years from Abraham's coming into the land of Canaan, and who must be now an hundred years old, being ninety nine at the time the Lord appeared unto him, and promised him a son at the set time the next year, Genesis 17:1 . This is observed, both to show the wonderful favour to Abraham, and the faithfulness of God in the exact performance of his promise: according to Bishop Usher F16 Annales Vet. Test. p. 9. , Isaac was born A. M. 2108, and before Christ 1896, and probably at Beersheba, see Genesis 21:33 .