Kauṣītaki (Śāṅkhāyana) Brāhmaṇa 3.6.15

3.6.15

tā vai gāyatrī triṣṭubhau bhavanti /

are the eye; the eye is threefold, white, black, and red. These offerings he does not perform in the animal or Soma sacrifice (thinking), 'Through the animal offering the Soma sacrifice is possessed of eyes; let me not make the sacrifice four-eyed and loathsome.' In that the invitatory verses contain the words 'to' and 'offered', and the offering verses the words 'forward', that is, 'given', verily thus having sacrificed he gives the oblation to the gods. These (verses) are Gāyatrī and Triṣṭubh; the Gāyatrī is the holy power; the Triṣṭubh is lordly power; verily thus with the holy and lordly power he gives the oblation to the gods. So great is the extension of the metre; verily thus with the whole extension of the metre he gives the oblation to the gods. At the end of the Ṛc he utters the sound *vaṣaṭ*; so do all his offering verses become beautiful. With *ṣaṭ* he utters *vaṣaṭ*; the seasons are six; verily thus he pleases the seasons. He should utter *vaṣaṭ* as connected with the Bṛhat and the Rathantara, with a long in front and short behind; the short is the Rathantara, the long the Bṛhat; again, the Rathantara is this (earth); the Bṛhat is yonder (sky); verily thus in these two he finds support. So great is the extension of speech; verily thus with the whole extension of speech he gives the oblation to the gods. '*bhūr bhuvaḥ*' he mutters before *ye yajāmahe*, 'Strength is might, might is strength; light' after the sound *vaṣaṭ*: the sound *vaṣaṭ* is a thunderbolt; verily thus he quietens it, both in front and behind. Strength and might are the two most dear forms of the sound *vaṣaṭ*; verily with them he quietens it.