Is Niqab Compulsory?
Question

Is wearing Niqab one of the conditions of Islamic dress for women?
Praise be to Allah.What is hijab?
Hijab in Arabic means covering or concealing. Hijab is the name of something that is used to cover. Everything that comes between two things is Hijab. 
Hijab means everything that is used to cover something and prevent anyone from reaching it, such as curtains, door keepers and garments, etc. 
What is khimar?
Khimar comes from the word khamr, the root meaning of which is to cover. For example, the Prophet (peace and blessings of Allah be upon him) said: “Khammiru aniyatakum (cover your vessels).” Everything that covers something else is called Khimar. 
But in common usage Khimar has come to be used as a name for the garment with which a woman covers her head; in some cases this does not go against the linguistic meaning of Khimar. 
Some of the jurists have defined it as that which covers the head, the temples and the neck. 
Difference between khimar and hijab
The difference between the Hijab and the Khimar is that the Hijab is something which covers all of a woman’s body, whilst the Khimar in general is something with which a woman covers her head. 
What is Niqab?
Niqab is that with which a woman veils her face (tantaqib)… 
Difference between Hijab and Niqab
The difference between Hijab and Niqab is that the Hijab is that which covers all the body, whilst Niqab is that which covers a woman’s face only. 
The woman’s dress as prescribed in shari’ah (“Islamic dress”) is that which covers her head, face and all of her body. 
Is niqab compulsory? 
But the Niqab or burqa’ – which shows the eyes of the woman – has become widespread among women, and some of them do not wear it properly. Some scholars have forbidden wearing it on the grounds that it is not Islamic in origin, and because it is used improperly and people treat it as something insignificant, demonstrating negligent attitudes towards it and using new forms of Niqab which are not prescribed in Islam, widening the opening for the eyes so that the cheeks, nose and part of the forehead are also visible. 
Therefore, if the woman’s Niqab or burqa’ does not show anything but the eyes, and the opening is only as big as the left eye, as was narrated from some of the salaf, then that is permissible, otherwise she should wear something which covers her face entirely. 
What is the prescribed hijab in Islam?
Shaykh Muhammad al-Salih al-‘Uthaymin (may Allah have mercy on him) said: 
“The Hijab prescribed in shari’ah means that a woman should cover everything that it is haram for her to show, i.e., she should cover that which it is obligatory for her to cover, first and foremost of which is the face, because it is the focus of temptation and desire. 
A woman is obliged to cover her face in front of anyone who is not her mahram (blood relative to whom marriage is permanently forbidden). From this we learn that the face is the most essential thing to be covered. 
There is evidence from the Book of Allah and the Sunnah of His Prophet (peace and blessings of Allah be upon him) and the views of the Sahabah and the imams and scholars of Islam, which indicates that women are obliged to cover all of their bodies in front of those who are not their mahrams.” (Fatawa al-Marah al-Muslimah, 1/ 391, 392) 
Should a woman cover her face?
Shaykh Salih al-Fawzan (may Allah preserve him) said: 
“The correct view as indicated by the evidence is that the woman’s face is ‘awrah which must be covered. It is the most tempting part of her body, because what people look at most is the face, so the face is the greatest ‘awrah of a woman. This is in addition to the shar’i evidence which states that it is obligatory to cover the face. 
For example, Allah says (interpretation of the meaning): 
“And tell the believing women to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts) and not to show off their adornment except only that which is apparent (like both eyes for necessity to see the way, or outer palms of hands or one eye or dress like veil, gloves, headcover, apron), and to draw their veils all over Juyoubihinna (i.e. their bodies, faces, necks and bosoms)…” [al-Nur 24:31] 
Drawing the veil all over the juyub implies covering the face. 
When Ibn 'Abbas (may Allah be pleased with him) was asked about the verse (interpretation of the meaning): “O Prophet! Tell your wives and your daughters and the women of the believers to draw their cloaks (veils) all over their bodies.” [al-Ahzab 33:59], he covered his face, leaving only one eye showing. This indicates that what was meant by the verse was covering the face. This was the interpretation of Ibn 'Abbas (may Allah be pleased with him) of this verse, as narrated from him by ‘Ubaydah al-Salmani when he asked him about it. 
Evidence for niqab from the Sunnah
In the Sunnah, there are many ahadith, such as: the Prophet (peace and blessings of Allah be upon him) said: “The woman in ihram is forbidden to veil her face (wear Niqab) or to wear the burqa’.” This indicates that when women were not in ihram, women used to cover their faces. 
This does not mean that if a woman takes off her Niqab or burqa’ in the state of ihram that she should leave her face uncovered in the presence of non-mahram men. Rather she is obliged to cover it with something other than the Niqab or burqa’, on the evidence of the hadith of ‘Aishah (may Allah be pleased with her) who said: “We were with the Prophet (peace and blessings of Allah be upon him) in ihram, and when men passed by us, we would lower the Khimar on our heads over our faces, and when they moved on we would lift it again.” 
Women in ihram and otherwise are obliged to cover their faces in front of non-mahram men, because the face is the center of beauty and it is the place that men look at… and Allah knows best.” (Fatawa al-Marah al-Muslimah, 1/396, 397) 
He also said: 
“It is OK to cover the face with the Niqab or burqa’ which has two openings for the eyes only, because this was known at the time of the Prophet (peace and blessings of Allah be upon him), and because of necessity. If nothing but the eyes show, this is fine, especially if this is customarily worn by women in her society.” (Fatawa al-Marah al-Muslimah, 1/399) 
And Allah knows best.