Śatapatha Brāhmaṇa ("of a hundred paths") 3.6.1.6

3.6.1.6

atha khanati | prāñcamutkaramutkirati yajamānena sammāyaudumbarīm parivāsayati tāmagreṇa prācīṃ nidadhātyetāvanmātrāṇi barhīṃṣyupariṣṭādadhinidadhāti

Thereupon he digs: eastwards he throws up the heap of earth. Having made the udumbara (post) of the same size as the sacrificer, he cuts it smooth all round, and lays it down, with the top to the east, in front (of the pit). Thereon he lays barhis-grass of the same length.