Śatapatha Brāhmaṇa ("of a hundred paths") 9.2.2.5

9.2.2.5

sa vai pañcagṛhītaṃ gṛhṇīte | pañcadhāvihito vā ayaṃ śīrṣanprāṇo mano vāk prāṇaścakṣuḥ śrotrametamevāsminnetatpañcadhāvihitaṃ śīrṣanprāṇaṃ dadhātyagnistigmena śociṣeti tigmavatyā śira evāsyaitayā saṃśyati tigmatāyai

He takes (ghee) in five ladlings, for fivefold divided is that vital air in the head,--the mind, speech, the breath, the eye, and the ear,--he thus lays that fivefold divided vital air into this head. [He offers it, with, Vâg. S. XVII, 16], 'Agni, with sharp flame, (may destroy every demon! Agni gaineth wealth for us)' thus with a (verse) containing (the word) 'sharp': he therewith sharpens his head so as to become sharp.