Śatapatha Brāhmaṇa ("of a hundred paths") 2.5.2.48

2.5.2.48

atha keśaśmaśrūptvā | samārohyāgnī udavasāyeva hyetena yajate na hi tadavakalpate yaduttaravedāvagnihotraṃ juhuyāttasmādudavasyati gṛhānitvā nirmathyāgnī paurṇamāsena yajata utsannayajña iva vā eṣa yaccāturmāsyānyathaiṣa kLptaḥ pratiṣṭhito yajño yatpaurṇamāsaṃ tatkLptenaivaitadyajñenāntataḥ pratitiṣṭhati tasmādudavasyati

Thereupon they shave (the sacrificer's) hair and beard; and take up the two fires,--for only after changing his place (to the ordinary sacrificial ground) he performs that (other) sacrifice, since it is not proper that he should perform the Agnihotra on the uttaravedi: for this reason he changes his place. Having gone to the house and 'churned out' the fires, he performs the full-moon offering. These seasonal offerings doubtless are detached sacrifices; whereas the full-moon offering is a regular, established sacrifice: hence he finally establishes himself by means of that regular sacrifice; and therefore he changes his place (to the ordinary sacrificial ground).