Śatapatha Brāhmaṇa ("of a hundred paths") 6.6.4.14

6.6.4.14

atha yadi prasuta āhavanīyo 'nugacet | gārhapatyaṃ vāva sa gacati gārhapatyāddhi sa āhṛto bhavati gārhapatyādevainam prāñcaṃ sāṃkāśinena hṛtvopasamādhāya prāyaścittīṃ karoti yastasminkāle 'dhvaraḥ syāttāmadhvaraprāyaścittiṃ kuryātsamānyagniprāyaścittiḥ

And if the Âhavanîya fire were to go out whilst the pressing (of Soma) proceeds, it is doubtless to the Gârhapatya that it goes, for from the Gârhapatya it has been taken. Having taken it straightway eastward from the Gârhapatya, and put fuel on it, he performs two expiations: whatever (kind of Soma) sacrifice may be (performed) at the time, the expiation of that sacrifice he should perform; and of like kind is the expiation of the fire-altar.