Jaiminīya (Talavakāra) Brāhmaṇa 2-8.343

Now, in the case of this pṛṣṭhya six-day period, that which is in the middle—

—they shift that seventeenfold day beyond the thirty-threefold [day].

Those who desire procreation should undertake this [rite].

The pṛṣṭhya six-day period is indeed procreation.

The stomas procreate with an increase by six; the meters with an increase by four.

Now this seventeenfold stoma, placed in the middle among the stomas that increase by six,

stands, as it were, obstructing procreation. When they shift it beyond the thirty-threefold [day], [it is with the intention]: 'May we procreate from unobstructed procreation.' And it is also to make a third to the two seventeenfold [stomas]. Then these two, Viśvajit and Abhijit, are the vital power on both sides of the stomas. By vital power, indeed, these two uphold the central day. Viśvajit and Abhijit are verily the two pegs of the sacrifice; by these two the sacrifice is upheld. Viśvajit and Abhijit are indeed the bed of the gods, and that Āditya is the royal power. Thus they place royal power upon the bed of the gods. Therefore, the ruler is mounted over the people. Then this twenty-first [day] is the central day. Twelve are the months, five the seasons, three these worlds; that Āditya is the twenty-first. They attain companionship in the same world with him; they ascend to him. Regarding this, they say: 'Those who ascend to this Āditya ascend to what is superior.' In that there is a reverse six-day period of this kind on the other side, it is for concealment, for non-injury, for auspiciousness, for peace. The concluding Atirātra is addressed to Vaiśvānara, for sacrifices lasting more than one day have their conclusion in Vaiśvānara.