Śatapatha Brāhmaṇa ("of a hundred paths") 2.1.1.2

2.1.1.2

athollikhati | tadyadevāsyai pṛthivyā abhiṣṭhitaṃ vābhiṣṭhyūtaṃ vā tadevāsyā etaduddhantyatha yajñiyāyāmeva pṛthivyāmādhatte tasmādvā ullikhati

In the first place he (the Adhvaryu) draws (three) lines (with the wooden sword on the Gârhapatya fire-place). Whatever part of this earth is either trodden or spit upon, that he thereby removes from it; and he thus establishes his fire on earth that is entirely proper for the sacrifice: this is why he draws lines (across the fire-place).