Śatapatha Brāhmaṇa ("of a hundred paths") 2.3.1.18

2.3.1.18

sa vai dviragnau juhoti | dvirupamārṣṭi dviḥ prāśnāti caturunnayati taddaśa daśākṣarā vai virāḍvirāḍvai yajñastadvirājamevaitadyajñamabhisampādayati

Twice he offers in the fire, twice he wipes (the spout of the spoon), twice he eats (of the milk), and four times he ladles;--these are ten (acts), for of ten syllables consists the virâg stanza, and the sacrifice is virâg (shining): he thereby converts the sacrifice into the virâg.