Śatapatha Brāhmaṇa ("of a hundred paths") 13.1.3.6

13.1.3.6

tadāhuḥ anāhutirvai rūpāṇi naitā hotavyā ityatho khalvāhuratra vā aśvamedhaḥ saṃtiṣṭhate yadrūpāṇi juhoti hotavyā eveti bahirdhā vā etamāyatanātkaroti bhrātṛvyamasmai janayati yasyānāyatane'nyatrāgnerāhutīrjuhoti

Concerning this they say, 'The Forms are no offering: they should not be offered.' But, indeed, they also say, 'Therein assuredly the horse-sacrifice becomes complete that he performs (the oblations relating to) the Forms: they should certainly be offered.' And, indeed, one puts that (Sacrificer) out of his resting-place, and raises a rival for him when one offers for him oblations elsewhere than in the fire, where there is no resting-place.