Conditions of
women’s niqaab
Question

                Is the niqab a pre-islamic custom if not
      what is the evidence (qur'an or hadith) to support the wearing of niqab, and is it
      preferred for sisters to wear the niqab? jazakumallaahu khairan.
Praise be to Allah.We have already spoken about the fact that it is obligatory for 
  women to cover their faces in Question #2198, 
  so please refer to that question.
With regard to the niqaab, this is a cover or veil 
  with a hole in it for the eyes. It is a way of dressing that was known to Muslim 
  women at the beginning of Islam, and it is mentioned in the hadeeth of the Prophet 
   (peace and blessings of Allaah be upon him) in 
  which he mentions what women in ihraam (for Hajj or Umrah) are not allowed 
  to do. He said: The woman in ihraam should not cover her face with a veil 
  or wear gloves. (Reported by al-Bukhaari, 1707). 
  Some of the scholars mentioned that a woman may uncover her left eye in order 
  to see where she is going, and if necessary she may uncover both eyes. The opening 
  should only be wide enough for the eyes, and the woman should beware of wearing 
  a niqaab with wide openings lest the beauty of her eyes becomes apparent and 
  the niqaab becomes a means of temptation instead of a veil covering her beauty 
  and adornment.