Short answer
Islam asks for modest, simple dress and good manners. No single garment is required. A man covers his body at least from the navel to the knee. A woman covers all but her face and hands in front of men outside her close family. Neither wears clothes that are see-through, skin-tight or made to draw attention. Men may not wear pure silk or gold. Muslims greet each other with "As-salamu alaikum", peace be upon you. The reply is "Wa alaikumus salam", and upon you be peace. Islam prizes keeping promises, telling the truth, justice and fair dealing. It asks Muslims to help the poor, honour parents and elders, love children and be good to neighbours. It forbids hatred, backbiting (speaking ill of someone behind his back), slander, mockery, insulting names, suspicion and arrogance.
Full explanation
Modest dress for men and women
The Qur'an says clothing was given to cover the body and to adorn it, and that the clothing of righteousness is best. It tells believing men and believing women alike to lower their gaze and guard their modesty. Women are told to draw their head-coverings over their chests. They are told not to show their adornment (their beauty and ornaments) beyond what ordinarily appears. Al-Tabari was a commentator on the Qur'an who died in 923. He reports that many early commentators explain what ordinarily appears as the face and the hands. He himself judged this the soundest reading. Most jurists (scholars of Islamic law) hold that a man must keep covered at least from the navel to the knee. Islam sets no uniform. Any clothing that meets these limits will do.
“O ye Children of Adam! We have bestowed raiment upon you to cover your shame, as well as to be an adornment to you. But the raiment of righteousness,- that is the best. Such are among the Signs of Allah, that they may receive admonition!”
“Say to the believing men that they should lower their gaze and guard their modesty: that will make for greater purity for them: And Allah is well acquainted with all that they do.”
“And say to the believing women that they should lower their gaze and guard their modesty; that they should not display their beauty and ornaments except what (must ordinarily) appear thereof; that they should draw their veils over their bosoms and not display their beauty except to their husbands, their fathers, their husband's fathers, their sons, their husbands' sons, their brothers or their brothers' sons, or their sisters' sons, or their women, or the slaves whom their right hands possess, or male servants free of physical needs, or small children who have no sense of the shame of sex; and that they should not strike their feet in order to draw attention to their hidden ornaments. And O ye Believers! turn ye all together towards Allah, that ye may attain Bliss.”
Al-Tabari reports from Ibn Abbas and others of the early generations that the adornment a woman may leave showing, "what ordinarily appears", is her face and her hands, and he judges this the soundest of the readings.
The Kuwaiti encyclopedia of Islamic law records that the great majority of jurists hold that the part of a man's body he must keep covered ('awra) is what lies between the navel and the knee.
What is not worn
The Prophet (ﷺ) warned of women who are clothed and yet appear naked. Scholars apply this to clothing that is see-through or so tight that it shows the shape of the body. He said gold and silk are lawful for the women of his community and forbidden to its men. He forbade men the gold ring. He said that whoever wears silk in this world will not wear it in the Hereafter.
Abu Hurayra reports that the Prophet (ﷺ) described two kinds of people of the Fire whom he had not yet seen: men with whips like the tails of cattle who beat people, and women who are clothed yet appear naked, leaning toward wrong and leading others to it.
Abu Musa reports that the Prophet (ﷺ) said: gold and silk have been made lawful for the women of my community and forbidden to its men.
Abu Hurayra reports that the Prophet (ﷺ) forbade the wearing of a gold ring.
Anas ibn Malik reports that the Prophet (ﷺ) said: whoever wears silk in this world will not wear it in the Hereafter.
Beauty without pride
Modest does not mean shabby. A man asked whether liking fine clothes and shoes was pride. The Prophet (ﷺ) said Allah (﷾) is beautiful and loves beauty. Pride, he said, is rejecting the truth and looking down on people. The Qur'an says Allah (﷾) does not love the arrogant boaster.
Abdullah ibn Mas'ud reports that the Prophet (ﷺ) said no one with an atom's weight of pride in his heart will enter Paradise. A man said that people like their clothes and shoes to be fine. The Prophet answered that Allah is beautiful and loves beauty; pride is rejecting the truth and looking down on people.
“"And swell not thy cheek (for pride) at men, nor walk in insolence through the earth; for Allah loveth not any arrogant boaster.”
The greeting of peace
The Prophet (ﷺ) taught that the greeting "As-salamu alaikum", peace be upon you, goes back to Adam. The angels answered it with more: peace and Allah's (﷾) mercy. The Qur'an tells Muslims to answer a greeting with a better one, or at least the same. The Prophet (ﷺ) said that spreading the greeting of peace makes people love one another. He said that one of the best deeds is to greet those you know and those you do not.
Abu Hurayra reports that the Prophet (ﷺ) said that when Allah created Adam, He told him to greet a group of angels and listen to their reply, for it would be the greeting of his children. Adam said "As-salamu alaikum" (peace be upon you), and they replied "As-salamu alaika wa rahmatullah" (peace and Allah's mercy be upon you), adding Allah's mercy.
“When a (courteous) greeting is offered you, meet it with a greeting still more courteous, or (at least) of equal courtesy. Allah takes careful account of all things.”
Abu Hurayra reports that the Prophet (ﷺ) said: you will not enter Paradise until you believe, and you will not believe until you love one another. He then said that the thing which makes people love one another is to spread the greeting of peace among them.
Abdullah ibn Amr reports that a man asked the Prophet (ﷺ) which deeds of Islam are best. He said: to feed people, and to greet those you know and those you do not know.
The virtues Islam prizes
The Qur'an commands Muslims to fulfil every promise. It tells them to stand firm for justice even against themselves, and not to let hatred of others make them unjust. It condemns those who cheat in weights and measures. It counts spending on the needy and the orphan as righteousness. It commands kindness and honour to parents in their old age. The Prophet (ﷺ) said truthfulness leads to Paradise. He told the youngest in a group to let the eldest speak first. He kissed his grandson, saying that whoever shows no mercy will be shown none. The angel Gabriel urged him to be good to neighbours so often that he thought neighbours would be made heirs.
“Come not nigh to the orphan's property except to improve it, until he attains the age of full strength; and fulfil (every) engagement, for (every) engagement will be enquired into (on the Day of Reckoning).”
“O ye who believe! stand out firmly for justice, as witnesses to Allah, even as against yourselves, or your parents, or your kin, and whether it be (against) rich or poor: for Allah can best protect both. Follow not the lusts (of your hearts), lest ye swerve, and if ye distort (justice) or decline to do justice, verily Allah is well-acquainted with all that ye do.”
“O ye who believe! stand out firmly for Allah, as witnesses to fair dealing, and let not the hatred of others to you make you swerve to wrong and depart from justice. Be just: that is next to piety: and fear Allah. For Allah is well-acquainted with all that ye do.”
“Woe to those that deal in fraud,- Those who, when they have to receive by measure from men, exact full measure, But when they have to give by measure or weight to men, give less than due.”
“It is not righteousness that ye turn your faces Towards east or West; but it is righteousness- to believe in Allah and the Last Day, and the Angels, and the Book, and the Messengers; to spend of your substance, out of love for Him, for your kin, for orphans, for the needy, for the wayfarer, for those who ask, and for the ransom of slaves; to be steadfast in prayer, and practice regular charity; to fulfil the contracts which ye have made; and to be firm and patient, in pain (or suffering) and adversity, and throughout all periods of panic. Such are the people of truth, the Allah-fearing.”
“Thy Lord hath decreed that ye worship none but Him, and that ye be kind to parents. Whether one or both of them attain old age in thy life, say not to them a word of contempt, nor repel them, but address them in terms of honour. And, out of kindness, lower to them the wing of humility, and say: "My Lord! bestow on them thy Mercy even as they cherished me in childhood."”
Abdullah ibn Mas'ud reports that the Prophet (ﷺ) said truthfulness leads to righteousness and righteousness to Paradise, and a man keeps telling the truth until he becomes truthful. Lying leads to wickedness and wickedness to the Fire, and a man keeps lying until he is recorded with Allah as a liar.
Rafi ibn Khadij and Sahl ibn Abi Hathma report that when a group of men came to the Prophet (ﷺ) about a killing, and the youngest of them began to speak, the Prophet said: let the eldest speak first.
Abu Huraira reports that the Prophet (ﷺ) kissed his grandson al-Hasan ibn Ali while al-Aqra ibn Habis was sitting with him. Al-Aqra said he had ten children and had never kissed any of them. The Prophet looked at him and said that whoever is not merciful to others will not be shown mercy.
Ibn Umar reports that the Prophet (ﷺ) said that Gabriel kept urging him to treat neighbours well, so much that he thought Gabriel would make neighbours heirs.
“Serve Allah, and join not any partners with Him; and do good- to parents, kinsfolk, orphans, those in need, neighbours who are near, neighbours who are strangers, the companion by your side, the wayfarer (ye meet), and what your right hands possess: For Allah loveth not the arrogant, the vainglorious;-”
What Islam condemns
The Qur'an forbids mocking others, defaming them and calling them by offensive nicknames. It tells believers to avoid suspicion, not to spy, and not to backbite. Backbiting is speaking ill of someone behind his back, and the Qur'an likens it to eating a dead brother's flesh. It pronounces woe on every slanderer and backbiter. It tells Muslims to shun those who profane the names of Allah (﷾). The Prophet (ﷺ) told Muslims not to hate or envy one another. He said that no one with an atom's weight of pride in his heart will enter Paradise.
“O ye who believe! Let not some men among you laugh at others: It may be that the (latter) are better than the (former): Nor let some women laugh at others: It may be that the (latter are better than the (former): Nor defame nor be sarcastic to each other, nor call each other by (offensive) nicknames: Ill-seeming is a name connoting wickedness, (to be used of one) after he has believed: And those who do not desist are (indeed) doing wrong.”
“O ye who believe! Avoid suspicion as much (as possible): for suspicion in some cases is a sin: And spy not on each other behind their backs. Would any of you like to eat the flesh of his dead brother? Nay, ye would abhor it”
“Woe to every (kind of) scandal-monger and-backbiter,”
“The most beautiful names belong to Allah: so call on him by them; but shun such men as use profanity in his names: for what they do, they will soon be requited.”
Anas ibn Malik reports that the Prophet (ﷺ) said: do not hate one another, do not envy one another, and do not turn your backs on one another; be servants of Allah, brothers. It is not lawful for a Muslim to cut off his brother for more than three days.
Abdullah ibn Mas'ud reports that the Prophet (ﷺ) said no one with an atom's weight of pride in his heart will enter Paradise. A man said that people like their clothes and shoes to be fine. The Prophet answered that Allah is beautiful and loves beauty; pride is rejecting the truth and looking down on people.
“"And swell not thy cheek (for pride) at men, nor walk in insolence through the earth; for Allah loveth not any arrogant boaster.”
Modesty in the New Testament
The New Testament also asks Christian women to dress modestly, with good works as their adornment. It goes further than Islam here, ruling out gold, pearls and costly dress for women. Modest dress is not foreign to the Bible. Muslim women keep in practice the modest dress that the Bible also asks for.
“In like manner also, that women adorn themselves in modest apparel, with shamefacedness and sobriety; not with broided hair, or gold, or pearls, or costly array; But (which becometh women professing godliness) with good works.”
Perspectives
The Islamic perspective
Islam asks both men and women to dress modestly and simply. It sets a few clear limits rather than a uniform. It teaches manners built on peace, truthfulness, justice and kindness. The Prophet (ﷺ) is the example for both.
The Qur'an tells believing men and women alike to lower their gaze and guard their modesty.
A woman covers all but her face and hands before men outside her close family. This is how many early commentators explain Qur'an 24:31.
Most jurists hold that a man covers at least from the navel to the knee.
Gold and silk are lawful for Muslim women and forbidden to Muslim men.
Clothing that leaves a woman clothed yet naked is condemned.
Muslims greet one another with the greeting of peace, and answer it with the same or better.
The Qur'an forbids mockery, offensive nicknames, suspicion, spying and backbiting.
Kindness to parents, neighbours and the needy is commanded alongside the worship of Allah (﷾).