Ancient writers were not negligent in preserving for us the correct pronunciation of the entire sacred name. Despite Jewish and Roman Church prohibitions against its use, the vocalization of the complete name was revealed and is preserved by some of these writers.
The following are various sources which attest to the pronunciation of the Tetragrammaton as Yahweh (Yah-oo-ay).
JOSEPHUS
Before any serious discussion can take place regarding the true pronunciation of the sacred name, it is necessary to recognize that the Tetragrammaton consists of four Hebrew vowels. Josephus writes:
His (the priest’s) head was covered by a tiara of fine linen, wreathed with blue, encircling which was another crown, of gold, whereon were embossed the sacred letters, to wit, FOUR VOWELS (φωνήεντα τέσσαρα; phonhenta tessara).1
CLEMENT OF ALEXANDRIA
Clement of Alexandria (2nd century CE), for instance, tells his readers that the sacred name was pronounced ’Ιαουέ and ’Ιαουαί,2 both words which approximate the sound Yah-oo-ay.