The Command “not to reveal their adornment"
“And to guard their private parts." The word farj is used in Arabic to refer to both a man and a woman's private parts. The fact that men and women have both been commanded to guard their modesty, to guard their private parts is in relation to two things: the view of others and this includes everybody except a husband and wife, and the other is that one should guard one's modesty from corruption, from adultery. If we look at the external form of the verse, perhaps we would conclude that it only refers to corruption but because, from the time of the Prophet's Companions and the very first commentaries on the Holy Quran, it has been clearly recorded that wherever the Holy Quran says, "guard their private parts," it means from adultery except in those verses where it is to guard the private parts from the view of others. Thus, this verse, either refers to the collective view or it refers to the view of others if we take the traditions into account. There is no difference of opinion here.
The third duty is not to reveal "their adornment..." which refers to that which is separate from the body like jewels and gold as well as things that are attached to the body like henna or collyrium.
As to the fact that they should "reveal not their adornment," there are two exceptions in the Holy Quran. The first is "except such as is outward" and the second is "except to their husbands...etc." Both of these have to be discussed further, in particular, the first exception.
Women should "not reveal their adornment... except such as is outward." What does this refer to? Is it beauty which is most often hidden under clothes that must not be revealed? Then what is that which "is outward?" From the beginning of Islam, many questions arose in relation to "except such as is outward" which were asked from the Companions of the Holy Prophet and the Helpers and many Shi'ites asked the pure Imams. There is almost total agreement regarding this point. That is, whether one is a Sunni who refers to the Companions and Helpers of the Holy Prophet or one be a Shi'ite who refers to the recorders of those traditions, there is more or less agreement that which "is outward" is collyrium, a ring and, in some, an anklet.
That is, adornments which are used on the two hands and the face. This then shows that it is not obligatory for women to cover their face or their hands. Things which adorn them may appear as long as they are part of common usage. The adornments which are applied to the hands and the face are not obligatory to be covered.
There are great many traditions in relation to this. It was asked from Imam Sadiq what may be displayed of adornments. That is, those things which are not obligatory to cover. He said, "It refers to collyrium and a ring and they are on the face and hands."  Abi Basir said he asked Imam Sadiq about the exception and he said a ring and bracelet." 
There is a tradition recorded by a person who was not a Shi'ite but because of his reliability, he is referred to and quoted by the ulama. He says that he heard from Imam Ja'far, peace be upon him, that the exception is the face and the hands. These are all similar in what they say. When the face and hands do not need to be covered, then their adornment, even more so.
There is another tradition narrated by Ali ibn Ibrahim from Imam Baqir, peace be upon him. He was asked about this exception and he said it includes a woman's clothes, collyrium, ring and coloring of the palms of the hands and a bracelet." 
Then the Imam said that we have three levels of adornment, the adornment all people may see, the adornment which mahram may see and the adornment for one's spouse. That which may be displayed for the people is the face and hands and their adornment such as collyrium, a ring, a bracelet but the adornment which may be displayed before someone who is mahram is the neck and above including a necklace, an armlet, hands plus an anklet and anything below the ankles.
There is, of course, a difference of opinion as to what can be revealed before someone who is mahram. That which can be concluded from the totality of the traditions and according to the edicts of the religious jurisprudents is that no one is mahram other than one's husband from the navel to the knees. That is, a woman must cover herself from the navel to the knee from even her father or brother and from the navel above, it must be covered from everyone except one's father. But for the husband, a woman may display her whole body.
We have other traditions in this area as well such as the fact that women must 'cast their veils over their bosoms'. Before the revelation of this verse, women would wear a scarf but they would place the ends behind their head so that their earrings, neck and chest would show since their dresses were most often v-necked. With the revelation of this verse, it became clear that they had to cover their ears, neck and chest with their head covering. There is a traditional recorded by Ibn Abbas, the well known transmitter of traditions, that it is obligatory for women to cover their chests and neck. 
The first exception we have referred to relates to what is not obligatory to be covered. The second exception refers to those before whom it is not obligatory to cover such as fathers, husbands, children, etc.
Is 'Looking’ Permissible For Men?
In this area there are two points to be recognized and separated, at least mentally. One is what is obligatory for women to cover and what is not. If we say that it is not obligatory for women to cover their face and hands, does this agree with the saying it is advisable for men to lower their gaze? Or is that something separate? Is it something which needs to be discussed separately? Is it possible that it is not obligatory for women to cover, even though this is definite in jurisprudence, but that it be advisable for men to lower their gaze?
We know from the life-style of the Holy Prophet that it is not obligatory for men to cover their head, hands, face or neck. Does this mean that it is also not advisable that men lower their gaze if they are walking down the street and women are passing? These are two different issues and must be discussed separately.
Another issue is that in areas other than the ones we mentioned as exceptions which the traditions have commented upon and in which the verse itself states what the limitations are, the face and the hands are among the absolute necessities of Islam whereby covering everything but them is obligatory for women. Of course, this itself has an exception which we will discuss in the next verse which is that if women reach beyond a certain age, it is no longer obligatory for them. But in general, covering the hair of a woman is among the compulsory precepts of Islam. It is clear that much of the hair which shows by which one would conclude that a woman's head is 'uncovered' is clearly not permissible to show in Islam. Covering the neck, the chest, the arms above the wrists, the feet (which is debated) from the ankles above are all among the obligatory aspects of Islam. There is no controversy here.
But there is another point. We said that we have to discuss separately whether or not lowering the gaze is advisable. If the look is of a flirting nature, looking with the anticipation of pleasure, this is another clear issue which is among those which are forbidden. Not only is it forbidden to look at strangers or persons to whom one is not mahram, but even those who are mahram as well. If a father was to flirt with his daughter, it is forbidden and perhaps an even greater sin. It is forbidden for a father-in-law to look at his son's wife with lust. That is, in Islam, lust is exclusively allowed between marital partners. It is not permissible in any form anywhere else between anyone else.
But this should be distinguished from riba' which means to look but not with the intention of lust nor to really see or view the other person. It is a special state which could be dangerous. That is, the fear exists that the look will cause a person to deviate to a forbidden state. This, then, is also forbidden and there is no difference of opinion on this.
Thus, if a person says it is advisable to look, a lustful look is not meant or a look which holds the fear that it may lead to something forbidden.
Now we will discuss 'looking'. We have a tradition recorded by Ali ibn Ja'far, the brother of Imam Riza. He asks to what point a man can look at a woman who is not permissible to him? He said, "Her face and her hands and her feet."  Of course, face and hands are clearly so but the jurisprudents have not issued edicts about the feet.
There is another tradition about a man who is on a trip and dies. There is no man present to give him the obligatory bath for the dead nor are any mahram women present. What should be done for the obligatory ritual bath? The opposite has also been questioned, a woman on a trip who dies and there are no mahram men present to give her bath. When in both cases they asked the Imam, Imam Sadiq said about the first case, "Those women may touch and wash that part of the man's body which was permissible for them to see when he was alive." The same thing is said about a woman who has died. The Imam said that if they touch the face and wash her face and her hands, this is sufficient. It is not necessary to wash her whole body. Thus, a man may look at a woman's face and hands when she is alive.' 
We also find this in the tradition in Mustamsak which Ayatullah Hakim relates about Fatimah, peace be upon her. One is the tradition regarding the Companion Salman who once entered her house and saw that she was grinding barley and her hands were bleeding. This tradition makes it clear that the hands were not covered and that it was not forbidden to look at her hands because if it had been, neither would Salman have looked at them nor would she have left them uncovered.
More authentic than this is a tradition of Jabir that appears in Kafi, in Wasa'il and in all of the reliable books on traditions which the ulama narrate. Jabir narrated that he went with the Prophet of God to enter the blessed Fatimah's house. The Holy Prophet had said that a person should seek permission to enter another's house, even if it belonged to one's mother and that the only exception is that one need not seek permission to enter one's wife's room. "When he arrived at her house, he did not enter but called out, 'Assalam alaykum ya ahl al-bayt'. She answered from inside the house. The Holy Prophet asked, 'Do you allow us to enter?' She said, Yes enter.' He asked, 'Should the person with mc enter?' She said, 'No. Then wait until I cover my head.' Then she said, 'Enter.' Again the Holy Prophet asked 'Should the person with me enter?' And she said, 'Yes.' Jabir says that when he entered he saw that her face was sallow colored. 'I became very sad when I realized it was because of lack of food. I said to myself, 'Look at how the caliph and a king's daughter is brought up and the daughter of Prophet of God!"' 
This shows that the Prophet's daughter neither covered her face nor her hands. Otherwise Jabir's look would have been forbidden.
Among the traditions, we have a great many which, when they ask of the Imam, he says that one cannot look at the forearm of a woman or at a woman's hair. All of these are mentioned but nowhere does it say anything about the face and hands.
Another issue is ihram (the pilgrim's clothes) where it is forbidden for women to cover their face and therefore we realize that it is not obligatory. It could not be that there be something which is obligatory but not so in the ihram and forbidden here.
"Let them cast their veils over their bosoms." The verse itself expresses the limits and does not include the face and hands. On the other hand, those who say looking' is absolutely forbidden have given a reason, the very reason which has been given for it not being forbidden. They refer to the verse, "say to the believing men to cast down their glance." He answers that in the first place, the verse does not say what not to look at. Secondly, it says min which mean 'from something', and thirdly, ghadd means 'cast down' or 'lower'.
There is another tradition which is referred to and those who say that it is forbidden to look should note it. A man wrote a letter to Imam Askari, peace be upon him, where he said that there is a woman who wants to confess something and others want to listen to her confession to bear witness to it. Must she confess behind a curtain and the others listen from behind a curtain to then justly say that it was her voice? The Imam said, "No. She should come forward to bear witness but she should cover herself so that only the roundness of her face shows.
Another tradition which they present is an often quoted tradition. It is called Sa'd Iskaf in reference to a man who went to the Prophet with his face bleeding and said that he had a complaint to make. The Holy Prophet told him to speak. He said he was walking down the street of Madinah and saw a woman coming towards him who was very beautiful and who had tied her scarf behind her head and her chest was visible. As she passed, he turned his head to look at her and did not see what was in front of him. Something was sticking out of the wall and it struck his face and injured him. The verse was then revealed, "Say to the believing men to cast down their glance." 
Another reason they give is that it says in the traditions, "Is there anything which has not committed an illicit act for the illicit act of the eyes is to look?" The answer is that this is referring to looking with lust, not just looking; like the tradition which says, "looking is like an arrow of satan," and, of course, it refers to looking with lust.
There is another tradition which I have read in the books on traditions of the Sunnis. It says the Holy Prophet was on a journey, probably the Farewell Pilgrimage. Ibn Abbas, a young boy then, was behind him. He continued to look at the women who passed back and forth in the ihram. The Holy Prophet realized that he was doing this and he turned the boy's face away. Ibn Abbas then began to look from that direction. The Holy Prophet again turned the boy's face away.
According to the Shi'ite sources, the tradition differs. It says that he was a very handsome young boy and the Holy Prophet was riding, probably on a camel. A woman from the Khasamiyyah tribe came to ask the Holy Prophet a question. She asked and the Holy Prophet answered. Then the Holy Prophet realized that her eyes were fixed upon Fazl ibn 'Abbas and Fazl ibn 'Abbas was staring at her. The tradition states that the Holy Prophet turned Fazl's face away saying, "A young woman and a young man, I am afraid satan will enter." 
They say that because of this, it is clear that it is forbidden to look like this. There is no doubt about it. This is love making and it is forbidden. Shaykh Ansari says that from this tradition it is clear that it was obligatory for women to cover themselves and it was not forbidden in general for men to look. Otherwise, the Holy Prophet would not have looked but he was looking at her as he was answering her questions and saw that her eyes were fixed on Fazl ibn 'Abbas and his on hers.
Ayatullah Hakim narrates another tradition. A man by the name of Ali ibn Salah said to Imam Riza, peace be upon him, "I have a problem. I look at beautiful women and it makes me happy to do so but I have no bad intentions." The Imam said, "There is no problem as God is aware of your intentions and you have no ill intentions but fear an illicit act."
. Kafi, vol. 5, p. 521 and Wasail, vol. 3, p. 25.
. Tafsir ul Quran, Safi, 24:31.
. Majma 'al‑Bayan, Quran 24:31.
. Qurb al‑Asnad, p.102.
. Wasa'il, vol.17, p.135.
. Kafi, vol. 5 p. 528 and Wasa'il, vol. 3, p. 28.
. Kafi, vol. 5, p. 521; al‑Wasail, vol. 3, p. 24. It should be noted that most often this Tradition which refers to a woman who tied her scarf around the back of her neck, lust and a man in general is also presented for verse 24:31. It would appear that it better relates to that verse.
. Sahih Bukhari, vol. 8, p.63.