Women appearing in front of men
Question

Many men in some families allow their wives, daughters and sisters to appear in front of men who are not their mahrams, such as their friends and colleagues, and let them sit with them and talk to them as if they were their mahrams. If we advise them they say that this is their custom and the custom of their forefathers, and they claim that their hearts are clean. Some of them are proud and arrogant although they understand the ruling, and others are ignorant of the ruling. What is your advice to them?.
Praise be to Allah.What every Muslim must do is not to rely on customs; rather he should refer the matter to the pure sharee’ah. Whatever Islam approves of is permissible and whatever it does not approve of, he should not do it. The fact that people are accustomed to a thing does not constitute evidence that it is permissible. All the customs that people may have in their cities or tribes should be referred to the Book of Allah and the Sunnah of His Messenger (peace and blessings of Allah be upon him). Whatever Allah and His Messenger have permitted is permissible, and whatever Allah has forbidden must be given up, even if it is the people’s custom. If the people are accustomed to being careless concerning the matter of khulwah (being alone with a non-mahram member of the opposite sex) or of women uncovering their faces in front of non-mahrams, these are false customs which must be given up. Similarly if people are accustomed to adultery, homosexuality and drinking alcohol, they must give up these things. What is customary does not count as proof, rather sharee’ah comes above all things, so the one whom Allah has guided to Islam has to keep away from that which Allah has forbidden of alcohol, adultery, theft, disobedience towards parents, severing the ties of kinship and everything that Allah has forbidden, and he must adhere to that which Allah has enjoined. 
Similarly the family must respect the command of Allah and His Messenger, and keep away from that which Allah and His Messenger have forbidden. If it is their custom for their women folk to appear in front of non-mahrams or to be alone with a non-mahram, they must give up those practices. 
A woman should not uncover her face or anything else in front of her cousin, her sister’s husband, or her husband’s brothers or uncles (paternal or maternal). Rather she must observe hijab and cover her face and head and entire body in front of any non-mahram. With regard to speaking, there is nothing wrong with that, such as returning the greeting of salaam or initiating it, so long as she observes hijab and avoids being alone with any non-mahram, because Allah says (interpretation of the meaning): 
“And when you ask (his wives) for anything you want, ask them from behind a screen, that is purer for your hearts and for their hearts” [al-Ahzaab 33:53] 
“O wives of the Prophet! You are not like any other women. If you keep your duty (to Allah), then be not soft in speech, lest he in whose heart is a disease (of hypocrisy, or evil desire for adultery) should be moved with desire, but speak in an honourable manner” [al-Ahzaab 33:32]
Allah forbade the wives of the Prophet (peace and blessings of Allah be upon him) to be soft in speech, i.e., to speak in a soft and alluring tone that might give hope to the one in whose heart is a disease, i.e., the disease of desire and make him think that she is easy and has no objections. Rather she should speak in a moderate tone that is neither too harsh nor too soft. And Allah tells us that hijab is purer for the hearts of everyone. 
And Allah says (interpretation of the meaning): 
“O Prophet! Tell your wives and your daughters and the women of the believers to draw their cloaks (veils) all over their bodies (i.e. screen themselves completely except the eyes or one eye to see the way). That will be better, that they should be known (as free respectable women) so as not to be annoyed. And Allah is Ever Oft-Forgiving, Most Merciful” [al-Ahzaab 33:59]
The jilbab (cloak, veil) is a garment which covers the head and body; the woman puts it over her head and covers her body with it, wearing it over her clothes. And Allah says (interpretation of the meaning): 
“And tell the believing women to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts) and not to show off their adornment except only that which is apparent (like both eyes for necessity to see the way, or outer palms of hands or one eye or dress like veil, gloves, headcover, apron), and to draw their veils all over Juyoobihinna (i.e. their bodies, faces, necks and bosoms) and not to reveal their adornment except to their husbands, or their fathers, or their husband’s fathers, or their sons, or their husband’s sons, or their brothers or their brother’s sons, or their sister’s sons, or their (Muslim) women (i.e. their sisters in Islam), or the (female) slaves whom their right hands possess, or old male servants who lack vigour, or small children who have no sense of feminine sex…” [al-Noor 24:31]
With regard to those mentioned in this verse, there is nothing wrong with a woman showing her adornment to them. 
So all Muslim women must fear Allah and avoid that which Allah has forbidden to them of showing their adornment to anyone other than those to whom Allah has permitted them to show it.