The Trinity in Jewish Tradition. The Sefer Y'TziRaH, The Book of Formation.

"The Three are One, and that One stands above." - Chapter IV, Section 3

"In thirty-two wonderful Paths of Wisdom did Yah, YHVH, the God of Israel, the Elohim of the living, the King of ages, the merciful and gracious God, the exalted One, the Dweller in eternity, most high and holy - engrave his name by the three Sepharim - Numbers, Letters, and Sounds." - Chapter I, Section 1

From The Sefer, Yetzirah