Śatapatha Brāhmaṇa ("of a hundred paths") 13.4.1.7

13.4.1.7

athāsmā adhvaryurniṣkam pratimuñcanvācayati tejo'si śukramamṛtamiti tejo vai śukramamṛtaṃ hiraṇyaṃ teja evāsmiñcukramamṛtaṃ dadhātyāyuṣpā āyurme pāhītyāyurevāsmindadhātyathainamāha vācaṃ yaceti vāgvai yajño yajñasyaivābhyārambhāya

The Adhvaryu then, hanging a gold ornament (nishka) round him, makes him mutter (Vâg. S. XXII, 1), 'Fire thou art, light and immortality,'--for gold, indeed, is fire, light, and immortality: fire (fiery mettle), light (brilliance), and immortality he thus bestows upon him;--'protector of life, protect my life!' he thereby bestows life (vital strength) upon him. With a view to commencing the sacrifice, he then says to him, 'Restrain thy speech!' for the sacrifice is speech.