Śatapatha Brāhmaṇa ("of a hundred paths") 9.4.2.15

9.4.2.15

atha vāruṇīṃ juhoti | atraiṣa sarvo 'gniḥ saṃskṛtaḥ sa eṣo 'tra varuṇo devatā tasmā etaddhavirjuhoti tadenaṃ haviṣā devatāṃ karoti yasyai vai devatāyai havirgṛhyate sā devatā na sā yasyai na gṛhyate vāruṇya 'rcā svenaivainametadātmanā svayā devatayā prīṇāti

He then offers one relating to Varuna. That whole Agni has now been completed, and he now is the deity Varuna: it is to him that he offers this oblation, and by the oblation he makes him (Agni) a deity, for that one alone is a deity to whom offering is made, but not that one to whom (offering is) not (made). With a verse addressed to Varuna (he offers): he thus gratifies him by his own self, by his own deity.