sister Shirin,
With all due respect, according to the scholars of Ahlus-Sunnah wal-Jam'aah, then there are clearly not many opinions on this subject.
As to the definition of the veil, from the verses of the Qur'aan, then there is a general agreement amongst the scholars that the covering of the women implies from head to toe. This explantion can be found in ibn Katheer's tafseer along with many other mufasireen (scholars of interpretation of the Qur'aan) of both past and present.
However, with regards to the exact details of veiling the hands and the face, then there are only two opinions which exist. Bringing into focus these two differences from prominent scholars of more recent times, Shaikh Ibn Baaz and Shaikh Uthaymeen (raheem ahumAllaah) are with the opinion that it is compulsory for the women to cover their hands and faces. One of the evidences being for this, that the wives of the Prophet (sallallaahu 'alayhi wa sallam) practiced this. They would veil their faces whenever they left their houses.
However Shaikh al-Albaani (raheemahullaah) has said that it is preffered for the females to cover their faces, but it is not obligatory. I don't know the exact evidence for this, but i have heard it is in light of Western and European situations, through analgy of various ahadeeth (Allaah knows best). This is the minimal requirement. Nevertheless, even though this is his opinion, it is known for his wife and daughters to cover themselves fully including the hands and the face.
So these are the two opinions. We can take either one, but we must be careful not to turn to a third, and try and stick by the scholars of understanding, who are, as the Prophet (sallallaahu 'alayhi wassalam) said the inheritors of the prophets.
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The Qur'an does not recommend any penalty/punishment for women who do not cover their heads. That is in itself significant.
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This may be so, but we know as Muslims, that when Allaah or His Messenger (sallallaahu 'alayhi wa sallam) command something, it becomes obligatory upon us as Muslims. And all obligations are to be sincerely fulfilled as far as possible. And we know that by not fulfilling such core commandments we become sinful. And we know that sinful matters lead to punishment (as the Prophet (saw) explained). And we know that if we escape punishment in this world, then we will receive it in the Hereafter, unless we sincerely repent for it (again as explained by the Prophet (saw)). So as Muslims, if we sincerely believe in Allaah and the Last Day, then we should try our utmost to follow his commandments if we wish to be free of all punishment - both of this world and the Hereafter.
... and Allaah knows best.
kind regards
"no leaf falls except that He knows of it, and no rain drop forms except that He has willed it."