Zohar 2:133b-134a

Jewish Mysticism
Once He is united above in six directions, so too, She is united below in six other directions, in order that everything will be one above and below, and it is said, “On that day, God will be one and His name one” (Zechariah 14-9). One above in six directions, as it is written, “shema yisrael YHWH eloheinu YHWH ehad” (Deut. 6-4), six words corresponding to six directions. One below in six directions, as it is written, “baruch shem kavod malkhuto le’olam va’ed,” six other directions in six words. YHWH ehad, [God is one] above, “u-shemo ehad” [and His name is one] below. And if you say that it is written “one” above, and below it is not written “one,” va-ed is ehad through and exchange of letters [hilufei atvvan], the letters of the male do not exchange. The letters of the feminine exchange, and this is the superiority of the male over the female. And in order to avoid the evil eye, we exchange the letters, so that we do not say ehad [one] openly. But in the time to come, when the evil eye will be removed from the world and it will hold no power, then it will be read ehad openly.

Translated by Hartley Lachter