The Kitáb-i-Aqdas - The Most Holy Book
Index term: Shaving the head
k44.
Shave not your heads; God hath adorned them with hair, and in this there are signs from the Lord of creation to those who reflect upon the requirements of nature. He, verily, is the God of strength and wisdom. Notwithstanding, it is not seemly to let the hair pass beyond the limit of the ears. Thus hath it been decreed by Him Who is the Lord of all worlds.
n68.
Shave not your heads
In some religious traditions it is considered desirable to shave one's head. The shaving of the head is forbidden by Bahá'u'lláh, and He makes it clear that the provision contained in His Súriy-i-Hajj requiring pilgrims to the Holy House in Shíráz to shave their heads has been superseded through this verse of the Kitáb-i-Aqdas (Q&A 10).
n69.
it is not seemly to let the hair pass beyond the limit of the ears
Shoghi Effendi has made clear that, unlike the prohibition on shaving the head, this law forbidding the growing of the hair beyond the lobe of the ear pertains only to men. The application of this law will require clarification by the Universal House of Justice.
q10.
 
Question: Shaving the head hath been forbidden in the Kitáb-i-Aqdas but enjoined in the Súriy-i-Hajj.
Answer: All are charged with obedience to the Kitáb-i-Aqdas; whatsoever is revealed therein is the Law of God amid His servants. The injunction on pilgrims to the sacred House to shave the head hath been lifted.