The ears cannot hear it; it is what makes the ears hear.
The eyes cannot see it; it is what makes the eyes see.
You cannot speak about it; it is what makes you speak.
The mind cannot imagine it; it is what makes the mind think.
It is different from what all we know; yet it is not known either.
Those who feel they know Him know Him not. Those who know that anything amenable to the senses is not Brahman, they know it best. When it is known as the innermost witness of all cognitions, whether sensation, perception or thought, then it is known.
One who knows thus reaches immortality.
- Kena Upanishad