Śatapatha Brāhmaṇa ("of a hundred paths") 10.6.1.9

10.6.1.9

atha hovāca janaṃ śārkarākṣyam sāyavasa kaṃ tvaṃ vaiśvānaraṃ vettheti divameva rājanniti hovācomiti hovācaiṣa vā atiṣṭhā vaiśvānara etaṃ hi vai tvamatiṣṭhāṃ vaiśvānaraṃ vettha tasmāttvaṃ samānānatitiṣṭhasi yo vā etamatiṣṭhāṃ vaiśvānaraṃ vedāpa punarmṛtyuṃ jayati sarvamāyureti mūrdhā tvā eṣa vaiśvānarasya mūrdhā tvāhāsyadyadi ha nāgamiṣya iti mūrdhā te'vidito'bhaviṣyadyadi ha nāgamiṣya iti vā

He then said to Gana Sarkarâkshya, 'O Sâyavasa, as whom knowest thou Vaisvânara?'--'As Heaven only, O king,' he replied.--'Yea,' he said, 'that indeed is Vaisvânara Pre-eminence; and because thou knowest the Vaisvânara Pre-eminence, therefore thou art pre-eminent among thine equals; and, verily, he who knows that Vaisvânara Preeminence repels death, and attains all life. But, indeed, this is only the head of Vaisvânara, and thy head would have failed thee, hadst thou not come hither; or the head would have been unknown to thee, hadst thou not come hither.'