Shatapatha Brahmana 2.6.3.16

2.6.3.16

athāyamanyatomukhaḥ puruṣaḥ | sa etatsarvatomukho bhavati yatparivartayate sa evamevānnādo bhavati yathaitāvetadya evaṃ vidvānparivartayate tasmādvai parivartayeta

This man, on the other hand, faces but one quarter; but by shaving his head all round he comes to face every quarter; and whosoever, knowing this, has his head shaved all round, becomes just such a consumer of food as those two: let him therefore have his head shaved all round.