Praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Niqab (Face veil) existed before the advent of Islam, was kept by Islam and enjoined by the Messenger of Allah (PBUH). This is supported by the following Hadith: Narrated `Abdullah bin `Umar: A person stood up and asked: "O Allah's: Apostle! What clothes may be worn in the state of Ihram?" The Prophet (PBUH) replie: "Do not wear a shirt or trousers, or any headgear (e.g. a turban), or a hooded cloak; but if somebody has no shoes he can wear leather stockings provided they are cut short off the ankles, and also, do not wear anything perfumed with Wars or saffron, and the Muhrima (a woman in the state of Ihram) should not cover her face, or wear gloves." {Related by Bukhari}.
Generally speaking, a woman`s clothes is indicated in the following verse: "And when ye ask (his ladies) for anything ye want, ask them from before a screen: that makes for greater purity for your hearts and for theirs. Nor is it right for you that ye should annoy God’s Apostle, or that ye should marry his widows after him at any time. Truly such a thing is in God’s sight an enormity." {Al-Ahzaab, 53}. This verse was revealed regarding the clothes that the mothers of the believers or the Prophet`s wives (Prohibited for all Muslims) wear when dealing with the companions, the best of this nation. By analogy, this code of dress should be followed by other women when dealing with men. Allah the Almighty Said (What means): " O Prophet! Tell thy wives and daughters, and the believing women, that they should cast their outer garments over their persons (when abroad): that is most convenient, that they should be known (as such) and not molested. And God is Oft- Forgiving, Most Merciful." {Al-Ahzab, 59}. Thus, the Hijab protects women from being molested.
Allah the Almighty also Said (What means): "And say to the believing women that they should lower their gaze and guard their modesty; that they should not display their beauty and ornaments except what (must ordinarily) appear thereof; that they should draw their veils over their bosoms and not display their beauty except to their husbands, their fathers, their husband’s fathers, their sons, their husbands’ sons, their brothers or their brothers’ sons, or their sisters’ sons, or their women, or the slaves whom their right hands possess, or male servants free of physical needs, or small children who have no sense of the shame of sex; and that they should not strike their feet in order to draw attention to their hidden ornaments. And O ye Believers! turn ye all together towards God, that ye may attain Bliss." {An-Nur, 31}.
Khimar is a long cape-like veil that covers the body until below the hips. It is tight-fitting around the head and leaves the face clear. The area below the woman`s chin can`t be covered save by drawing the veil over the bosom.
Most of the scholars are agreed on this matter and a Muslim woman who wears Niqab or Khimar has done what is permissible and is on the safe side as far as the teachings of Sharia are concerned and. And Allah The Almighty Knows Best.