Shatapatha Brahmana 14.3.1.24

14.3.1.24

sa vai na sarvamivānayet nedyajamānātparāgannamasadityardham vā bhūyo vā pariṣinaṣṭi tasminnaparāhṇe yajamānāya vratamabhyutsicya prayacati tadyajamāna evaitadannādyaṃ dadhāti tatho ha yajamānānna parāgannam bhavati

Let him not pour in all (the milk), lest the food should turn away from the Sacrificer.--He leaves over half of it or more; and on that same afternoon he pours it to the fast-milk, and hands it to the Sacrificer: thereby he bestows food upon the Sacrificer, and thus, indeed, food does not turn away from the Sacrificer,