māṇḍūkya upaniṣad

Om. May we hear auspicious words with our ears, O Gods; may we see auspicious sights with our eyes, O venerable ones. May we, with steady limbs and bodies, enjoy the full span of life allotted by the Divine. May Indra, of ancient glory, grant us well-being; may Pūṣan, the all-knowing, grant us well-being; may Tārkṣya, the protector of all, grant us well-being; and may Bṛhaspati grant us well-being. Om, peace, peace, peace. Hariḥ Om. Om is this Imperishable Sound; all that has been, is, and shall be is truly Om. And whatever is beyond the reaches of time is also truly Om.

All this is indeed Brahman. This Ātman is Brahman, and this Ātman possesses four aspects.

The first aspect is Vaiśvānara, whose sphere is the waking state, who is conscious of the external world, who possesses seven limbs and nineteen mouths, and who experiences gross objects.

The second aspect is Taijasa, whose sphere is the dream state, who is conscious of the internal world, who possesses seven limbs and nineteen mouths, and who experiences the subtle impressions of the mind.

That is the state of deep sleep where the sleeper desires no objects and beholds no dreams. This is the third aspect, Prājña, whose sphere is deep sleep, in whom all experiences become unified, who is a mass of pure consciousness, who is filled with bliss, who experiences bliss, and who is the gateway to the awareness of the other two states.

He is the Lord of all, the Knower of all, the Inner Controller; He is the source of all, the origin and the dissolution of all beings.

The fourth is not conscious of the internal world, nor the external world, nor both; it is not a mass of consciousness, nor is it conscious, nor unconscious. It is unseen, beyond action, incomprehensible, uninferable, unthinkable, and indescribable. Its essence is the firm belief in the unitary Self; it is the cessation of all phenomena, tranquil, auspicious, and non-dual. This is the Ātman, and this is what must be realized.

That same Ātman is, in the realm of sound, represented by Om, corresponding to its letters. The aspects of the Self are the measures of the sound, and the measures are the aspects of the Self: namely, the letters A, U, and M.

Vaiśvānara, who dwells in the waking state, is the first letter, A, because of its all-pervasiveness and because it is the beginning. One who knows this attains all desires and becomes the first among all.

Taijasa, who dwells in the dream state, is the second letter, U, because of its superiority and its intermediate nature. One who knows this exalts the flow of knowledge, becomes equal-minded, and in his lineage, no one ignorant of Brahman is born.

The state of deep sleep is Prajna, the third quarter, which corresponds to the letter 'M'. Just as one measures a grain heap or as all things merge into the whole during dissolution, so too does the one who knows this truth realize that all existence is measured within the Self and ultimately dissolves into It.

The fourth state is the partless Om, which transcends all worldly transactions and phenomena. It is the cessation of the relative world, all-auspicious, and non-dual. Thus, Om is indeed the Atman itself. He who realizes this truth enters into the Supreme Self through his own Self.