Śatapatha Brāhmaṇa ("of a hundred paths") 3.1.2.3

3.1.2.3

taddhaike | sarva eva vapante sarva eva medhyā bhūtvā dīkṣiṣyāmaha iti tadu tathā na kuryādyadvai keśaśmaśru ca vapate nakhāni ca nikṛntate tadeva medhyo bhavati tasmādu keśaśmaśru caiva vapeta nakhāni ca nikṛnteta

Now some shave themselves all over, in order that they may be consecrated after becoming pure all over; but let him not do this. For even by shaving the hair of his head and his beard, and by cutting his nails, he becomes pure: let him therefore shave only the hair of his head and his beard, and cut his nails.