Śatapatha Brāhmaṇa ("of a hundred paths") 1.5.2.2

1.5.2.2

yajamāna eva juhūmanu | yo smā arātīyati sa upabhṛtamanu sa yaddve iva brūyādyajamānāya dviṣantam bhrātṛvyam pratyudyāminaṃ kuryādattaiva juhūmanvādya upabhṛtamanu sa yaddve iva brūyādattra ādyam pratyudyāminaṃ kuryāttasmādekāmivaivāha

The Sacrificer, doubtless, stands behind the guhû, and he, who means evil to him, stands behind the upabhrit; and if he were to speak of two (spoons), he would cause the spiteful enemy to countervail the Sacrificer. Behind the guhû stands the eater, and behind the upabhrit the one to be eaten; and if he were to speak of two (spoons), he would make the one to be eaten countervail the eater. For these reasons he speaks of one (spoon) only.