Śatapatha Brāhmaṇa ("of a hundred paths") 2.4.2.9

2.4.2.9

sa jaghanena gārhapatyam | prācīnāvītī bhūtvā dakṣiṇāsīna etaṃ grṛhṇāti sa tata evopotthāyottareṇānvāhāryapacanaṃ dakṣiṇā tiṣṭhannavahanti sakṛtphalīkaroti sakṛdu hyeva parāñcaḥ pitarastasmātsakṛtphalīkaroti

While seated behind the Gârhapatya, with his face turned toward the south, and the sacrificial cord on his right shoulder, he takes that (material for the offering from the cart). Thereupon he rises from thence and threshes (the rice) while standing north of the Dakshina fire and facing the south. Only once he cleans (the rice); for it is once for all that the fathers have passed away, and therefore he cleans it only once.