Jaiminīya (Talavakāra) Brāhmaṇa 2-3.34

2-3.34

tadāhuryatṣaṭkṛtvaḥ purastādviṣuvataḥ pṛṣṭhyānyupayanti viṣvajiti
saptamamupariṣṭātkathaṃ tatsabhāramiti
sa brūyādyadvā arvācīnaṃ viṣuvatastadayaṃ loko yadūrdhvaṃ viṣuvatastadasau lokaḥ
āsanna iva vā ayaṃ lokaḥ
prarikta ivāsāvanyaḥ
dvitīyo hyayaṃ lokaḥ
tadyadviśvajiti saptamamupariṣṭātpṛṣṭhyānyupayantyevaṃ sabhāramiti
atho ya evaṃ viśvajitpṛṣṭhamayameva
gaurvai rathataramaśvo bṛhadajā vairūpamavirvairājaṃ vrīhayaśśakvaryo yavā revatayaḥ
sa eṣa rathassaṃsakto yatpṛṣṭhāni
tasyaiṣo'kṣo yadgāyatrīṣu bṛhadagniṣṭomasāma bhavatyetasya rathasyānapavyāthāya
atha ya etannirhṛtapṛṣṭhamupayanti viṣaktarathaṃ te viśvajitaṃ śūnyamupayanti
te na kiṃ cana vyaśnuvate
tasmātpṛṣṭhamaya eva viśvajitkārya iti

In this regard they say: 'Whereas they undertake the pṛṣṭhyas six times before the Viṣuvat, and the seventh after it on the Viśvajit, how is that of equal weight?' He should say: 'What is on this side of the Viṣuvat is this world; what is beyond the Viṣuvat is that world. This world is as if near; that other is as if empty; for this world is second. In that they undertake the pṛṣṭhyas on the Viśvajit as the seventh afterwards, thus it has equal weight.' Moreover, he who [performs] the Viśvajit in this way, it consists entirely of pṛṣṭhas. The cow is Rathantara; the horse is Bṛhat; the goat is Vairūpa; the sheep is Vairāja; rice is Śakvarī verses; barley is Revatī verses. The pṛṣṭhas are this fully assembled chariot. That the Bṛhat is the Agniṣṭoma-sāman on Gāyatrī verses is the axle of this chariot, for the non-breakdown of this chariot. Now those who undertake this with its pṛṣṭha removed, they undertake the Viśvajit as an unyoked chariot, empty; they do not attain anything. Therefore the Viśvajit should be made to consist entirely of pṛṣṭhas.