Jaiminīya (Talavakāra) Brāhmaṇa 2-8.360

Now this is of the form of a three-day period. There are indeed three seasons; the others are non-seasons. Summer, the rainy season, and winter: these are indeed the prosperous seasons; the others are as if attached to them. [They do this] so that: 'Those seasons which are prosperous, they shall be obtained by us.' There are indeed three meters, three pressings, three [breaths]—in-breath, out-breath, and diffused breath—and these three worlds. Whatever is three-fold, this is the prosperity of all that, the attainment thereof. There are five three-day periods beyond, and five on this side. By that very fact they do not depart from the nature of a five-day period. Now this Viśvajit is an Atirātra having all pṛṣṭhas; it is a day belonging to Prajāpati. Day and night are the complete Prajāpati: 'May we prosper in the complete Prajāpati, may the complete Prajāpati be obtained by us.' Regarding this, they say: 'Those who undertake this Viśvajit Atirātra ascend to what is superior, for they approach Prajāpati manifestly.' Then, that there are five three-day periods coming backward beyond it is just for conciliation, for freedom from affliction, for auspiciousness, for peace. The concluding Atirātra is connected with Vaiśvānara; for ahīna soma sacrifices have Vaiśvānara as their conclusion.

This sacrificial session consists of three months; by that, whatever is prosperity, that very thing is prosperity.

The two months which [make up] a season are its prosperity.

The season, manifestly, is the prosperity of the year.