Shatapatha Brahmana 11.1.7.3

11.1.7.3

tadāhuḥ kimayanamiti svayaṃ haivaite rātrī agnihotraṃ juhuyātsa yaddhutvā prāśnāti tenāpitṛdevatyo bhavatyāhutirvā eṣā sa yadevaitāmātmannāhutiṃ juhoti teno eteṣām medhānāṃ nāśnāti

As to this they say, 'What course of procedure is there?' Well, let him, on those two nights (of full and new moon), himself offer the Agnihotra: inasmuch as, after offering, he takes food he does not become consecrated to the Fathers, for that (libation) is an offering; and inasmuch as he performs that offering in his own self he does not eat of those sacrificial essences.