Śatapatha Brāhmaṇa ("of a hundred paths") 13.4.1.13

13.4.1.13

tasyai pañcadaśa sāmidhenyo bhavanti pañcadaśo vai vajro vīryaṃ vajro vajreṇaivaitadvīryeṇa yajamānaḥ purastātpāpmānamapahate vārtraghnāvājyabhāgau pāpmā vai vṛtraḥ pāpmano'pahatyā agnirmūrdhā divaḥ kakudbhuvo yajñasya rajasaśca netetyupāṃśu haviṣo yājyānuvākye mūrdhanvatyanyā bhavati sadvatyanyaiṣa vai mūrdhā ya eṣa tapatyetasyaivāvaruddhyā atha yatsadvatī sadevāvarunddhe virājau saṃyājye sarvadevatyaṃ vā etaccando yadvirāṭ sarve kāmā aśvamedhe sarvāndevānprītvā sarvānkāmānāpnavānīti hiraṇyaṃ dakṣiṇā suvarṇaṃ śatamānaṃ tasyoktam brāhmaṇam

For this (offering) there are fifteen kindling-verses; for fifteenfold is the thunderbolt, and the thunderbolt means vigour: with the thunderbolt (of) vigour the Sacrificer thus from the first repels evil. The two butter-portions relate to the slaying of Vritra, with a view to the repelling of evil, for Vritra is evil. [The verses, Vâg. S. XIII, 14, 15,] 'Agni, the head, the summit of the sky...,' and 'Be thou the leader of the sacrifice and the realm of space (whither thou strivest with auspicious teams: thy light-winning head hast thou raised to the sky, and thy tongue, O Agni, hast thou made the bearer of the offering),' pronounced in a low voice, are the anuvâkyâ and yâgyâ of the chief oblation. The one contains (the word) 'head,' the other (the verb) 'to be,'--for the head, assuredly, is he that shines yonder: thus it is in order to secure him (the Sun); and as to why (the other) contains (the verb) 'to be,'--he thereby secures that which is (the real, truly existent). The Samyâgyâs are two virâg-verses; for that--to wit, the Virâg--is the metre belonging to all the gods, and all objects of desire are (contained) in the Asvamedha: 'Having gratified all the gods, may I obtain all my desires!' so he thinks. The sacrificial fee is gold weighing a hundred (grains): the meaning of this has been explained.