Jaiminīya (Talavakāra) Brāhmaṇa 25.148

Now the Iṣovṛdhīya having an external finale (bahirnidhana), belonging to the Bṛhat. Therefore it is performed on the Bṛhat day. The sixth day is for nourishment (iṣ); the seventh is for growth (vṛdh). From the sixth day indeed the seventh day is produced. In that [they say] 'iṣaḥ', thereby they generate the seventh day from the sixth day. In that [they say] 'vṛdhaḥ', because now they grew, as it were. Prajāpati created creatures. He created them without food, without food. Becoming hungry, they ate one another. That Prajāpati reflected: 'How indeed may these creatures of mine not hunger?' He saw this sāman. With it he touched them with the words 'iṣovṛdhīya'. Anointed with food, they grew for him. That is the nature of the Iṣovṛdhīya as Iṣovṛdhīya. Anointed with food indeed his dependents prosper who knows thus. It has a four-syllable finale. Cattle indeed are four-footed. Cattle are this day; it is indeed for the obtainment of cattle.

'Being cleansed by nimble hands, in the ocean thou speedest the voice, wealth'—

with [the syllable] 'ru', it is the form of the Revatīs.

'Thou gushest abundantly with yellow hue, broad and bountiful, O Pavamāna'—

'Purifying thyself through the sheep's wool filter, the bull Pavamāna roared in the wood'—

thus [the verses] contain the word 'bull' (vṛṣan), which is the form of the Bṛhat.

This day belongs to the Bṛhat.