Śatapatha Brāhmaṇa ("of a hundred paths") 11.2.7.28

11.2.7.28

saṃsthā sūktavākaḥ sa yo ha vai saṃsthā sūktavāka iti vedāva ha saṃsthāṃ runddhe'tho yatkiṃ ca saṃsthayā jayyaṃ sarvaṃ haiva tajjayati gacati vayasaḥ saṃsthām

The Sûktavâka is the completion; and, verily, whosoever knows the Sûktavâka to be the completion secures for himself the completion; and whatever is to be gained by the completion all that he now gains: he obtains the completion of his (full) lifetime.