This is the tribe which took its origin and had its name from Ishmael, the son of Abraham; and the ancients called them Ishmaelites after their progenitor. As their mother Hagar was a slave, they afterwards, to conceal the opprobrium of their origin, assumed the name of Saracens, as if they were descended from Sara, the wife of Abraham. Such being their origin, they practice circumcision like the Jews, refrain from the use of pork, and observe many other Jewish rites and customs. If, indeed, they deviate in any respect from the observances of that nation, it must be ascribed to the lapse of time, and to their intercourse with the neighbouring nations. Moses, who lived many centuries after Abraham, only legislated for those whom he led out of Egypt. The inhabitants of the neighboring countries, being strongly addicted to superstition, probably soon corrupted the laws imposed upon them by their forefather Ishmael. The ancient Hebrews had their community life under this law only, using therefore unwritten customs, before the Mosaic legislation. These people certainly served the same gods as the neighbouring nations, honouring and naming them similarly, so that by this likeness with their forefathers in religion, there is evidenced their departure from the laws of their forefathers. As is usual, in the lapse of time, their ancient customs fell into oblivion, and other practices gradually got the precedence among them.
Salminius Hermias Sozomenus, Ecclesiastical History, Book VI.