Śatapatha Brāhmaṇa ("of a hundred paths") 1.4.1.13

1.4.1.13

sa ha naiva pratiśuśrāva | taṃ tvā ghṛtasnavīmaha ityevābhivyāharadathāsya ghṛtakīrtāvevāgnirvaiśvānaro mukhādujjajvāla tam na śaśāka dhārayituṃ so 'sya mukhānniṣpede saimām pṛthivīm prāpādaḥ

Still he did not answer. (The priest continued), 'Thee, O butter-sprinkled one, we invoke! (Rig-veda V, 26, 2);' so much he uttered, when at the very mentioning of butter, Agni Vaisvânara flashed forth from the (king's) mouth: he was unable to hold him back; he issued from his mouth, and fell down on this earth.