Chandogya Upanishad 3.15

The chest which has the sky for its circumference and the earth for its bottom, does not decay, for the quarters are its sides, and heaven its lid above. That chest is a treasury, and all things are within it.

Its eastern quarter is called Guhtû, its southern Sahamânâ, its western Râgñî, its northern Subhûtâ. The child of those quarters is Vâyu, the air, and he who knows that the air is indeed the child of the quarters, never weeps for his sons. 'I know the wind to be the child of the quarters, may I never weep for my sons.'

'I turn to the imperishable chest with such and such and such.' 'I turn to the Prâna (life) with such and such and such.' 'I turn to Bhûh with such and such and such.' 'I turn to Bhuvah with such and such and such.' 'I turn to Svah with su ch and such and such.'

'When I said, I turn to Prâna, then Prâna means all whatever exists here — to that I turn.'

'When I said, I turn to Bhûh, what I said is, I turn to the earth, the sky, and heaven.'

'When I said, I turn to Bhuvah, what I said is, I turn to Agni (fire), Vâyu (air), Âditya (sun).'

'When I said, I turn to Svah, what I said is, I turn to the Rig-veda, Yagur-veda, and Sâma-veda. That is what I said, yea, that is what I said.'