The Mandukya Upanishad
English version copied from James Swartz

Om, the Word, is all this, a clear explanation of which follows: all that is past, present, and future is Om.
Whatever is before the past and after the future is Om.

All this is the Limitless I. This Self is the limitless I.

The first quarter (of the Self) is the waker whose field is the waking state, who is conscious of the external world of objects,
who has seven limbs and nineteen mouths, and who enjoys the world’s gross objects.

The second quarter is the dreamer whose field of experience is the dream state, who is conscious of the internal world of objects,
who has seven limbs and nineteen mouths and who enjoys the subtle objects of the dream world.

The third quarter is the sleeper in whom all experiences become undifferentiated into a mass of consciousness,
and who is the gateway to the waking and dream states.
In the deep sleep state the sleeper neither sees or desires subtle or gross objects.

The sleeper is the Lord of all manifest existence.
It is the knower of all, the inner controller, and the source of all.
The sleep state is that from which all things originate and into which they all dissolve.

The Self is known as “the fourth” and is to be realized.
It is neither conscious of the external or internal worlds, nor is it a mass of consciousness.
It is not simple consciousness, nor is it unconscious.
It cannot be seen by the senses, is unrelated to anything, incomprehensible to the mind, uninferable, unthinkable, and indescribable.
It’s nature is pure consciousness, the negation of all phenomena, non-dual, blissful, and peaceful.

Viewed as sounds the Self is A, U, M.

The one who meditates on the waking state as “A,” the first and most pervasive, fulfills all desires and becomes a leader.

The one who meditates on the dream state as “U” because it is between and superior, attains superior knowledge
and is treated fairly by all.
In his line of descendants everyone attains Self knowledge.

The one who meditates on the sleep state as “M” as the measure and
that wherein all things become one is able to realize the nature of things
and beings and understand all things within himself.

That which is partless, soundless, incomprehensible, beyond the senses, blissful, non-dual
and that wherein all phenomena are resolved is the “forth,” the Self.
The one who knows It dissolves the self in It.