Śatapatha Brāhmaṇa ("of a hundred paths") 3.7.1.7

3.7.1.7

atha barhīṃṣi | prācīnāgrāṇi codīcīnāgrāṇi cāvastṛṇāti pitṛṣadanamasīti pitṛdevatyaṃ vā asyaitadbhavati yannikhātaṃ sa yathānikhāta oṣadhiṣu mitaḥ syādevametāsvoṣadhiṣu mito bhavati

Thereupon he strews barhis-grass therein, both eastward-pointed and northward-pointed, with, 'Thou art the seat of the Fathers!' for that part of it (the stake) which is dug into the ground is sacred to the Fathers: as though it were (naturally) established among plants, and not dug in, so does it become established among those plants.