Śatapatha Brāhmaṇa ("of a hundred paths") 1.2.1.1

1.2.1.1

sa vai kapālānyevānyatara upadadhāti | dṛṣadupale anyatarastadvā etadubhayaṃ saha kriyate tadyadetadubhayaṃ saha kriyate

Now the one (viz. the Âgnîdhra) puts the potsherds on (the Gârhapatya fire); the other (viz. the Adhvaryu) the two mill-stones (on the black antelope skin): these two acts are done simultaneously. The reason why they are done simultaneously (is this):