Śatapatha Brāhmaṇa ("of a hundred paths") 6.4.4.18

6.4.4.18

dvābhyāmupāvaharati | dvipādyajamāno yajamāno 'gniryāvānagniryāvatyasya mātrā tāvataivainametadupāvaharati taṃ dakṣiṇata udañcamupāvaharati tasyokto bandhuruddhatamavokṣitam bhavati yatrainamupāvaharatyuddhate vā avokṣite 'gnimādadhati sikatā upakīrṇā bhavanti tāsāmupari bandhuḥ

With two (verses) he takes it down,--two-footed is the Sacrificer, and the Sacrificer is Agni: as great as Agni is, as great as is his measure, with so much he thus takes it down. He takes it down from the right (south) to the left (north) side: the significance of this has been explained. Raised and sprinkled is (the place) where he takes it down, for on a (mound), raised and sprinkled, the (sacrificial) fire is laid down. Gravel is strewed thereon: the significance of this (will be explained) hereafter.