Shatapatha Brahmana 9.2.1.12

9.2.1.12

yadvevainaṃ samukṣati | atraiṣa sarvo 'gniḥ saṃskṛtastasmindevā etadrūpamuttamamadadhustathaivāsminnayametadrūpamuttamaṃ dadhātyannaṃ vai rūpametadu paramamannaṃ yaddadhi madhu gṛtaṃ tadyadeva paramaṃ rūpaṃ tadasminnetaduttamaṃ dadhāti sarvataḥ samukṣatyapi bāhyena pariṣritaḥ sarvata evāsminnetadrūpamuttamaṃ dadhāti darbhaiste hi śuddhā medhyā agrairagraṃ hi devānām

And, again, as to why he sprinkles him;--here that Agni has been built up complete: on him the gods now bestowed the highest (or last) form; and in like manner does this (Sacrificer) now bestow on him the highest (or last) form; but form means food, and these, to wit, sour curds, honey and ghee, are the most excellent kind of food: this, the most excellent form he thus bestows upon him as his highest (property). Everywhere he sprinkles, even outside the enclosing-stones; everywhere he thus bestows on him the highest form;--by means of sacrificial grass-stalks (he sprinkles), for they are pure and meet for sacrifice; by means of their tops (he sprinkles), for the top (is sacred) to the gods.