Shatapatha Brahmana 1.6.1.20

1.6.1.20

tadāhuḥ | kiṃdevatyānyājyānīti prājāpatyānīti ha brūyādanirukto vai prajāpatiraniruktānyājyāni tāni haitāni yajamānadevatyānyeva yajamāno hyeva sve yajñe prajāpatiretena hyuktā ṛtvijastanvate taṃ janayanti

Here now some say, 'To what deity belong the butter-portions?' Let him reply, 'To Pragâpati;' for, assuredly, Pragâpati is undefined (mysterious); and undefined are the butter-portions, because they have the sacrificer for their deity; for the sacrificer is Pragâpati at his own sacrifice, since it is by his order that the priests spread and produce it.