Jaiminīya (Talavakāra) Brāhmaṇa 5.18

The Śāktyas, having meat-cake [offerings], performed a sacrificial session. Gaurīvīti Śāktya killed a deer. Tārkṣya Suparṇa swooped down upon it from above. He aimed [his arrow] at him. He said to him: "Seer, do not shoot at me! I shall tell you tomorrow's [knowledge]. Today indeed you know, but not tomorrow." To him he revealed this Gaurīvita. Thence he saw tomorrow. Tomorrow is offspring; tomorrow is cattle; tomorrow is the heavenly world. That the Gaurīvita is performed is for the obtaining of all this, for the attainment of this. The sap of speech overflowed; that became the Gaurīvita. Since the Gaurīvita is performed day after day, day after day they go placing the sap of speech. If any should omit the Gaurīvita in an ahīna rite, one should tell them: "You will be without a tomorrow, without offspring." Without a tomorrow and without offspring they indeed become.

Then the Tvāṣṭrī-sāman has its finale in the middle for firm support. Truly, they float out into a fathomless ocean who undertake the Ārbhava Pavamāna. That it has its finale in the middle is for firm support. In front of that finale they undertake the pratihāra. By the prastāva and the pratihāra the sacrificer is held fast. Running away as it were is this day, which is the ninefold (trivṛt). That they undertake the pratihāra before the finale is indeed to prevent slipping down. Indra, having hurled the thunderbolt at Vṛtra and thinking "I have not laid [him] low," entered the cows. They desired: "May we give birth to Indra!" They saw these sāmans, the Tvāṣṭrī-sāmans. With them they gave birth to Indra. These indeed are sāmans that generate a hero. A hero is born to him who knows thus. Moreover, the Tvāṣṭrīs are cattle. That these sāmans are used is for the obtaining of cattle. It has an iḷā-finale; cattle are iḷā, for the obtaining of cattle. Since the cows of Tvaṣṭṛ (Tvāṣṭrī) saw it, therefore it is called Tvāṣṭrīsāma. "Toward the dear [seats] he flows, placed in delight"—[the word] "toward" (abhi) is the form of the Rathantara. Belonging to the Rathantara is this day.