Shatapatha Brahmana 2.2.4.6

2.2.4.6

sā hainamabhirādhayāṃ cakāra | sa vyacikitsajjuhavānī3 mā hauṣā3miti taṃ svo mahimābhyuvāda juhudhīti sa prajāpatirvidāṃ cakāra svo vai mā mahimāheti sa svāhetyevājuhottasmādu svāhetyeva hūyate tata eṣa udiyāya ya eṣa tapati tatoyam prababhūva yo 'yam pavate tata evāgniḥ parāṅ paryāvavarta

This (offering) then satisfied him. He hesitated: 'Shall I offer it up? shall I not offer it up?' he thought. His own greatness said to him, 'Offer it up!' Pragâpati was aware that it was his own (sva) greatness that had spoken (âha) to him; and offered it up with 'Svâhâ!' This is why offerings are made with 'Svâhâ!' Thereupon that burning one (viz. the sun) rose; and then that blowing one (viz. the wind) sprang up; whereupon, indeed, Agni turned away.