Śatapatha Brāhmaṇa ("of a hundred paths") 10.3.3.2

10.3.3.2

vetthāgnimiti hovāca kimeva mā vidvānupodasada ityagniṃ vedeti kamagniṃ vettheti cakṣuriti yastamagniṃ veda kiṃ sa bhavatīti cakṣuṣmānbhavatīti hovāca nainaṃ cakṣurjahātīti

'Thou knowest Agni,' he said; 'knowing what (else) hast thou come to me?'--'Agni I know.'--'What Agni knowest thou?'--'The Eye.'--'What becomes of him who knows that Agni?'--'He becomes seeing,' he said; his eye does not fail him.'