The command of concealing ones satr has remained ever present in all Divine religions. In fact, when Adam and Hawa ‘alaihimassalaam were stripped of their clothing while still in Jannah they began to cover themselves with the leaves of Jannah. Concealing ones satr is part of the fitrah – primordial nature of humans and was an obligation right from the advent of Islam. In contrast, the command of hijab did not exist in most Divine religions and in the early era of Islam but was first revealed in the third or fifth year of Hijrah.

Not only is the veiling of the face established in Islam, it is also based on concrete evidences. This has been the continuous practise of the ummah for the past fourteen centuries. As the great scholar of Al-Azhar, Hafidh Ibn Hajar al-Asqalani has said,

ولم تزل عادة النساء قديما وحديثا يسترن وجوههن عن الاجانب

“It has continuously been the practice of women since time immemorial to cover their faces from strangers.”(Fath al-Bari 9/324)

It is with great sadness that we note some confusion in the minds of certain students and even some scholars, concerning the obligation of the niqab (veil) according to the Hanafi madhab. The Hanafi madhab expressly classifies covering the face as binding on women and forbids the exposure of the face in the presence of ghair mahrams (strangers).

Rather Imam al-Haramayn (d. 478 AH) said: “There exists consensus of the Muslims on preventing women from emerging with their faces uncovered.”

 قال إمام الحرمين الجويني (ت ٤٧٨ ه): اتفق المسلمون على منع النساء من الخروج سافرات الوجوه

In this link one may download three papers which deal with the issues of satr, hijab and niqab in Shariah. A must read for all students of Deen.