Śatapatha Brāhmaṇa ("of a hundred paths") 3.5.4.20

3.5.4.20

so 'vanayati | rakṣohaṇo vo valagahano 'vanayāmi vaiṣṇavānityatha barhīṃṣi prācīnāgrāṇi codīcīnāgrāṇi cāvastṛṇāti tadyānīmāni prāṇeṣu lomāni tānyevaitaddadhāti tasmādeṣu prāṇeṣvimāni lomāni

He pours it out with, 'You, the Rakshas-killers, the charm-killers, Vishnu's own, I pour out.' Thereupon he spreads barhis-grass, both such as is turned with its tops to the east and such as is turned to the north; what hair there is here at (the openings of) the vital airs, that he thereby bestows: hence that hair at (the openings of) the vital airs.