Shatapatha Brahmana 1.4.5.6

1.4.5.6

yajamāna eva dhruvāmanu | yo 'smā arātīyati sa upabhṛtamanu sa yaddhopabhṛtā samaṇjyādyo yajamānāyārātīyati tasmiṃcriyaṃ dadhyāttadyajamāna evaitacriyaṃ dadhāti tasmāddhruvayā samanakti

The sacrificer, assuredly, stands behind the dhruvâ, and he who means evil to him stands behind the upabhrit. Hence if he were to mix (the butter remaining in the guhû) with (that in) the upabhrit, he would bestow excellence on him who means evil to the sacrificer; but in this, way he bestows that excellence on the sacrificer himself: for this reason he mixes (the butter in the gull with (that in) the dhruvâ.