Shatapatha Brahmana 13.2.1.2

13.2.1.2

ājyena juhoti tejo vā ājyaṃ tejasaivāsmiṃstattejo dadhātyājyena juhotyetadvai devānām priyaṃ dhāma yadājyam priyeṇaivaināndhāmnā samardhayati

With ghee he makes offering, for ghee is fiery mettle: by means of fiery mettle he thus lays fiery mettle into him (the horse and Sacrificer). With ghee he offers; for that--to wit, ghee--is the gods’ favourite resource: it is thus with their favourite resource he supplies them.