Zohar 2:69b.

Jewish Mysticism
“And the angel of the Lord [sc. Shekhinah] appeared to him [Moses] in a flame of fire out of the midst of a thorn bush” (Exod. 3-2)- “The thorn bush [i.e., the demonic potency] was surely within that holiness [i.e., Shekhinah] and cleaving to it, for everything cleaves together, the pure and the impure; there is no purity except from within impurity. This is the mystery, ‘Who can bring a pure thing from what is impure’ (Job 14-4). The shell and the kernel are together.”

Translated by Elliot Wolfson in “Light Through Darkness- The Ideal of Human Perfection in the Zohar,” Harvard Theological Review 81 (1988)- 73-95.