Jaiminīya (Talavakāra) Brāhmaṇa 2-3.44

This heavenly world is indeed the Mahāvrata day. It is twenty-five-fold. Of that, the twenty are the virāj; then the four are these four quarters; then the twenty-fifth is this upward quarter. Where the quarters rose together, there arose this world named Atyagra, which shines yonder. By this twenty-fifth [stoma] they ascend to this very [world]; they attain fellowship in the world with it. Regarding this they say: 'Since by this day—by the Mahāvrata—they desire to obtain the most, why then is this restraining twenty-five-fold stoma performed?' One should reply: 'For the obtaining of all food.' With five stoma verses he obtains man, with five cattle, with five the horse, with five the goat, with five the sheep. Thus this twenty-five-fold stoma is performed at the end for the obtaining of all food. Now, as for the two Atirātras, they are the firm support. Having found firm support in this world through the introductory Atirātra, they set out; having found firm support in that world through the concluding Atirātra, they rise up. They become, as it were, flourishing; they stand firm.

Now, there is this royal throne of udumbara wood.

Some set it down facing east.

One should set it down facing north.

Its two intermediate corners are the front legs, these two the hind [legs].

Some mount it facing east.

Regarding this, Śāṭyāyani said: 'Facing north they perform the priestly service of the sāman;'

'the Udgātṛs have the north as their deity;'

'it is facing north that one should mount it.'