mentioned in DN15
There are beings who, having transcended the Sphere of Infinite Consciousness, thinking: “There is no thing”, have attained to the Sphere of No-ningness. That is the seventh station of consciousness. [The two realms are:] The Realm of Unconscious Beings and, secondly, the Realm of Neither-Perception-Nor-Non-Perception. (Bodhi)
In DN24 there is some more info:
2.20. 'There are, Bhaggava, some ascetics and Brahmins who declare that the beginning of things was due to chance. I went to them and asked them if this was their view. “Yes”, they replied. I asked them how this came about, and when they could not explain, I said: "There are, friends, certain devas
called Unconscious. As soon as a perception arises in them, those devas fall from that realm. . .remembering nothing (Sutta, I , verse 2.31) they think: 'Now from non-being I have been
brought to being.’ That, Reverend Sirs, is how it comes about that you teach that the beginning of things was due to chance."
DN33 also mentions them §3.2
(3) 'Nine abodes of beings (a) Beings different in body and different in percep&ion, (b) beings different in body and alike in perception, (c) beings alike in body and different in perception, (d) beings alike in body and alike in perception, (e) the Realm of Unconscious Beings, (f) the Realm of Neither-Perception-
Nor-Non-Perception, (g) beings who have attained to the Sphere of Infinite Space, (h) beings who have attained to the Sphere of Infinite Consciousness, (i) beings who have attained to the Sphere of No-Thingness (as Sutta 15, verse 33).