Zohar Hadash, 38b

Jewish Mysticism
Commenting on “In the center of the fire the likeness of the hashmal” (Ezek. 1-4)-

It has been established that [the word hashmal refers to] the fiery beasts that speak, and they are the splendor the shines, it goes up and down, the fire that is burning. It exists and does not exist, for there is no one who can understand it in one place. No eyes or vision can master it. It is and it is not, in one place and then in another place. It goes up and down. In this appearance is hidden that which is hidden and concealed that which is concealed. This is the mystery called hashmal. Prophets must see, know, and contemplate within this with the vision of the heart and eye more than anything else … All that they contemplate to see and to know is the speculum that does not shine. No prophet merited to contemplate the speculum that shines but Moses, the faithful prophet, for all the keys of the house were placed in his hand. When all the other prophets reached this hashmal to contemplate with their eyes, their thoughts were confused and the heart was not settled, and because of it they abandoned all corporeal images. Consequently, they saw within what they saw in silence.

Translated by Elliot Wolfson in Through a Speculum that Shines- Vision and Imagination in Medieval Jewish Mysticism, Princeton- Princeton University Press, 1994.