Shatapatha Brahmana 11.1.7.4

11.1.7.4

ete ha vai rātrī sarvā rātrayaḥ samavayanti yā āpūryamāṇapakṣasya rātrayastāḥ sarvāḥ paurṇamāsīṃ samavayanti yā apakṣīyamāṇapakṣasya rātrayastāḥ sarvā amāvāsyāṃ samavayanti sa yo haivaṃ vidvāntsvayamupavasathe juhoti sarvadā haivāsya svayaṃ hutam bhavati

Now all the nights concentrate themselves in these two nights: all the nights of the waxing moon concentrate in the night of full moon, and all the nights of the waning moon concentrate in the night of new moon; and, verily, for him who, knowing this, offers (the Agnihotra) himself on the day of the entrance on the fast, offering is always made by himself.