Question: Is it necessary for a muslim woman to cover her face with a veil, or is it sufficient for her to wear a hijaab that covers her head and a jilbab to cover her entire body?
Answer: If there is a Khaliifah and he orders women to cover their faces, then they must do so by scholarly consensus (ijmaa^). This is the consensus that is mentioned by Nawawiy and others that people think is an unconditional consensus. In reality, however, the basic religious order is to cover everything except the face and hands with something that covers the color of the skin. This is the duty today, because there is no Khaliifah. Some scholars, such as Maalik and Abuu Yusuf said that part of the lower arm may also be shown, and Abu Haniifah said that the feet may be shown below the ancle. This is because it may be difficult to keep these areas covered at all times. One may not have socks for example.
Most scholars, particularly the Hanafis, will argue that because we live in very corrupt times, it is a duty for women to cover their faces in public. This is to avoid the sins that showing her face may lead to from others (looking at her with desire etc.).
However, there is no basis for this in the sayings of the founders of the school. Moreover, Al-Sarkhasi, the author of Al-Mabsoot, the main book for relating the sayings of the scholars of the Hanafi school, explicitly states in this book that it is not a duty for a woman to cover her face, even if there is fear of fitnah. Finally, in one incidence, Prophet Muhammad,-may Allah raise his rank- turned the head of a man so that he would not look at a beautiful woman because he feared that this looking would lead the man to sin. Yet, he did not order her to cover her face. Some will argue that this is a special case, because it was during pilgrimage, but this is weak, because a woman may cover her face in pilgrimage with something that does not come in contact with her face, as the Prophet't wives used to do. Moreover, the Prophet said explicitly that he feared fitnah and that is why he turned the man's head away from looking. It is therefore pointless to argue that there is no fear of fitnah during pilgrimage.
... and Allah knows best.