The second principle: The entirety of the Divine reality, in relation to the creation of the souls and their modes of existence, are discerned by us on the following three levels: a) Ein Sof, blessed be He; b) the world of Atzilut; c) the three worlds that are called Beria, Yetzira, and Asiya. Understand that the Zohar deals only with the worlds of Beria, Yetzira, and Asiya, and also with Ein Sof, blessed be He, and the world of Atzilut to the extent that Beria, Yetzira, and Asiya receive from them, but as for Ein Sof, blessed be He, and the world of Atzilut as they are in themselves, the Zohar does not engage with them at all.
Infinite and Finite of Asiya
Baal HaSulam's Preface to Zohar 4:1