Jaiminīya (Talavakāra) Brāhmaṇa 2-8.338

Now, these [nights] contain the twelve-day rite. For indeed, the sacrifice of the gods, the sacrifice of Prajāpati, is this twelve-day rite. / By this sacrificial session, indeed, Prajāpati prospered. Thinking, 'By that sacrificial session by which Prajāpati prospered, let us prosper,' [they perform it]. / Regarding this, they say: 'What is the summit of sacrificial sessions?' / 'The twelve-day rite,' he should say. / The twelve-day rite, indeed, is the summit of sacrificial sessions; for in no other sacrificial session is there a forty-four-verse stoma, nor a forty-eight-verse [stoma]. / Thinking, 'Let that which is the summit of sacrificial sessions be undertaken by us,' [they perform it]. / And indeed, here and there they employ speech in diverse ways, those who sacrifice, those who sit for a sacrificial session. / That [speech] they bring to completion precisely with the tenth day. / Thinking, 'May we attain the conclusion of complete speech, not pulled apart, firmly established,' [they perform it]. / And by one sacrificial session they undertake two sacrificial sessions: the twelve-day rite and the fourteen-night rite. / The concluding Atirātra is sacred to Vaiśvānara; for non-soma-sacrificial periods have their conclusion in Vaiśvānara.

This sacrificial session indeed belongs to a single month.

The prosperity through that is precisely this prosperity.

A month, indeed, revolving again and again, attains the year.

It is the year that they wish to obtain, the year they desire to attain, when they sacrifice, when they sit for a sacrificial session.

For there is nothing whatsoever outside the year.

Autonomous rule, indeed, are these nights which are fifteen.

Seven days are on that side, seven on this side.

Now, the day which is in the middle, that is autonomous rule, that is the heavenly world.

Thus they go to the zenith of the sun, thus they go to autonomous rule.