Brahma Vidhya Upanishad
Introduction:Sariram as the body of the sound OM As such are mentioned:
Body of the Sound - Three Vedas: Three Fires : Three Worlds : Three Gods
a- Rig - Grahapatya Earth Brahman
u- Yajur - Dakshina Mid-region Vishnu
m- Sama Ahavaniya Heaven Siva
I proclaim the Brahman-love, which is omniscience, which is the highest; It shows as origination and end Brahman, Vishnu, Mahesvara.
Vishnu, working with his miraculous power becomes, at intervals, a human being through compassion, His secret, as the OM fire, lies in the Brahman lore.
The syllable OM is the Brahman. Thus, verily, teach the Brahmanknowers; Body, location, time and dying away of this syllable, I will proclaim.
I The body or sariram of the sound OM:
There are three gods and three worlds, three Vedas and three fires. Three Moras and the half mora. In that trisyllabic, blissful one.
The Rig Veda, Grahapatya. The earth and Brahman as God, That is the body of the a sound, as expounded by the Brahman-knowers.
The Yajur Veda and the mid-region, and the fire Dakshina, and the holy god Vishnu, This is the u sound proclaimed to us.
The Sama Veda and heaven, the Ahavaniya fire also, and Iswara, the highest (or supreme) god, thus is the m sound proclaimed to us.
II The location or sthaanam of the sound OM:
In the midst of the brain-conch, like the sun-shine glitters the a; within it is situated, the u sound of moon-like splendor.
The m sound too, like the fire, smokeless, resembling a lightning flash Thus shine the three moras, like the Moon, the Sun and the fire.
There upon a pointed flame, like a torch light exists; know it as the half mora, which one writes above the syllable.
III The terminus or kaala of the sound OM:
Yet one, like a pointed flame subtle, like lotus-fibre, shines the Sun-like cerebral artery (passing through it) penetrates (the OM).
Through the Sun and seventy two thousand arteries, breaks through the head - and remains as bringer of blessings to all pervading the whole Universe.
IV The vanishing, fading away or layaa of the sound OM:
And just as the sound of a metal utensil or of a gong dies in silence so he, who seeks the All lets the OM sound fade away in silence.
For that wherein the sound fades away Is the Brahman, the higher yea, the whole sound is Brahman And conduces to immortality.
Om Shanti ! Shanti ! Shanti !