Shatapatha Brahmana 3.8.2.15

3.8.2.15

tadupāsyābhitiṣṭhati | idamahaṃ rakṣo 'bhitiṣṭhāmīdamahaṃ rakṣo 'vabādha idamahaṃ rakṣo 'dhamaṃ tamo nayāmīti tadyajñenaivaitannāṣṭrā rakṣāṃsyavabādhate tadyadamūlamubhayataḥ paricinnam bhavatyamūlaṃ vā idamubhayataḥ paricinnaṃ rakṣo 'ntarikṣamanucarati yathāyam puruṣo 'mūla ubhayataḥ paricinno 'ntarikṣamanucarati tasmādamūlamubhayataḥ paricinnam bhavati

Having thrown it away (on the utkara), he treads on it with, 'Herewith I tread down the Rakshas! herewith I drive away the Rakshas! herewith I consign the Rakshas to the nethermost darkness!' Thus it is by means of the sacrifice that he drives away the evil spirits, the Rakshas. And as to its being rootless and severed on both sides,--rootless, forsooth, and severed on both sides, the Rakshas moves about in the air, even as man here moves about in the air rootless and severed on both sides: therefore it (the grass-end) is rootless and severed on both sides.