Surah 14. Ibrahim, Ayah 39

Abraham was 100 years old when Isaac was born (Gen. xxi. 5); and as Isma'il was 13 years old when Abraham was 99. (Gen. xvii. 24-25), Isma'il was also a son of his father's old age, having been born when Abraham was 86 years old. The younger son's progeny developed the Faith of Israel and that of Christ; the elder son's progeny perfected the more universal Faith of Islam, the Faith of Abraham the True.