Śatapatha Brāhmaṇa ("of a hundred paths") 9.2.3.6

9.2.3.6

āśuḥ śiśāno vṛṣabho na bhīma iti | aindryo 'bhirūpā dvādaśa bhavanti dvādaśa māsāḥ saṃvatsaraḥ saṃvatsaro 'gniryāvānagniryāvatyasya mātrā tāvataivaitaddakṣiṇato 'surānrakṣāṃsi nāṣṭrā apahanti triṣṭubbhirvajro vai triṣṭubvajreṇaivaitaddakṣiṇato 'surānrakṣāṃsi nāṣṭrā apahanti tā dvāviṃśatirgāyatryaḥ sampadyante tadāgneyyo bhavantyagnikarma hi

'The swift (Indra), sharpening (his weapon), like a terrible bull,'--these are twelve suitable (verses) relating to Indra,--a year consists of twelve months, and Agni (the fire-altar) is the year: as great as Agni is, as great as is his measure, by so much he drives off the Asuras, the mischievous fiends, in the south. With trishtubh (verses he does so),--the Trishtubh is the thunderbolt: by the thunderbolt he thus drives off the Asuras, the mischievous fiends, in the south. They amount to twenty-two Gâyatrîs, and thus they relate to Agni, for this is Agni's performance.