Hijab For Awrah

Awrah

The Arabic word awrah refers to the parts of the body which must be covered with clothing. Awrah is any part of the body, for both men and women, which may not be visible to the public. Awrah is interpreted differently depending upon the sex of the company one is in.
Men

Most Muslims accept that for men everything between the navel and the knee is awrah and therefore should be covered at all times.
Women

Rules for women are more complicated. There are a number of scenarios for women:

    In front of unrelated men (Muslim or non-Muslim), women must cover everything except the hands and face
    In front of close male relatives, awrah is the navel to the knee and the stomach and the back
    In front of other Muslim females, awrah is from the navel down to, and including, the knees
    Awrah in front of non-Muslim women is a point of debate:
        Some scholars say that women should cover all but the hands and face. This is to prevent non-Muslim women (who may not understand the rules regarding hijab) from describing the appearance of the hijab wearer to other men
        Other scholars say that if a non-Muslim woman can be trusted not to describe a woman's appearance to other men, then she may reveal as much as she would in front of another Muslim woman in her presence.

The Hanafi school of thought, which is followed by most Muslims in the world, agree that the feet are not part of the awrah and therefore may be revealed.

Amongst other schools of thought a common opinion is that everything apart from a woman's face and hands is awrah. Scholars holding this opinion use this hadith to justify it:

    Narrated Aisha (the Prophet's wife): Asma, daughter of Abu Bakr, entered upon the Apostle of Allah (peace be upon him) wearing thin clothes. The Apostle of Allah (peace be upon him) turned his attention from her. He said: 'O Asma, when a woman reaches the age of menstruation, it does not suit her that she displays her parts of body except this and this, and he pointed to her face and hands.

    Abu Dawud, Book 32, Number 4092

N.B.: This particular hadith is regarded as 'weak' (i.e. not reliably attributed) by some scholars, including the hadith's collector, Abu Dawud.
Husband and wife

There is no restriction on what a husband and wife may show to each other in private. The Qur'an encourages married couples to enjoy each other's bodies.
Individuals in private

Islam highly values modesty, so even when alone, men and women are recommended never to be completely naked and to cover from the navel to the knee. Exceptions do apply where necessary, for example taking a shower or going to the bathroom.