Principal Upanishad · Rigveda
Aitareya Upanishad 3.3
Prajnanam Brahma — consciousness is Brahman
प्रज्ञानं ब्रह्म।
Consciousness is Brahman.
What this verse points to
Three words, and one of the four mahavakyas — the one drawn from the Rigveda. Not "consciousness perceives Brahman" or "leads to" it. The copula is doing the entire work.
What makes it usable rather than abstract is that consciousness is the one thing never absent from your experience. Whatever the statement points to, it cannot be somewhere you are not.
Sit with it
Notice that you are aware. Then notice that the awareness has not changed in quality since you were a child.
About the Aitareya Upanishad
A short Upanishad on the emergence of the world and of the person from the Self. It carries the mahavakya prajnanam brahma — "consciousness is Brahman" — one of the four great statements drawn one from each Veda.
References to this text are given as chapter.verse — here, 3.3.