Śatapatha Brāhmaṇa ("of a hundred paths") 1.4.1.19

1.4.1.19

tadu kathamabhūditi | yatraiva tvaṃ ghṛtasnavīmaha ityabhivyāhārṣīstadeva me ghṛtakīrtāvagnirvaiśvānaro mukhādudajvālīttaṃ nāśakaṃ dhārayituṃ sa me mukhānnirapādīti

'How then did this happen?'--'At the moment when thou didst utter the words, "(Thee), O butter-sprinkled one, we invoke!" just then, at the mention of butter, Agni Vaisvânara flashed forth from my mouth; I was unable to hold him back, he issued from my mouth.'