Monotheism in Jewish Writings: Philo I
And God said, “At first say unto them, I am that I am, that when they have learnt that there is a difference between him that is and him that is not, they may be further taught that there is no name whatever that can properly be assigned to me, who am the only being to whom existence belongs”.
On the Life of Moses
On the Life of Moses, 75
p. 466
Philo. (1993). The Works of Philo: Complete and Unabridged (C. D. Yonge, Trans.). Hendrickson Pub. http://books.google.co.uk/books?id=PDy2AAAACAAJ&hl=&source=gbs_api