The Holy Quran has ordered the women to cover themselves in some situations.
"And say to the believing women that they cast down their looks and guard their private parts and do not display their ornaments except what appear thereof. And let them wear their head coverings over their bosoms, and not display their ornaments..." (Surah Nur 24:31)
It is also mentioned in Surah Ahzab, "O Prophet ! Say to your wives and daughters and the women of the believers that they let down upon them their over garments, this will be more proper, that they may be known and thus they will not give trouble. And Allah is Forgiving, Merciful."
(Surah Ahzab 49:59)
In the same chapter, Allah says:-
"O wives of the Prophet ! You are not like any other of the women, if you will be on your guard, then be not soft in (your) speech, lest he whose heart has a disease yearn and speak a good word."
(Surah Ahzab 49:32)
Another verse "And when you ask them (the wives of the Prophet) any goods, ask of them from behind a curtain, this is purer for your hearts and (for) their hearts."(Surah Ahzab 49:53)
In the above verses, the Muslim woman is ordered to veil herself. She must not come before na mehram without Hijab. She should dress in such a manner that strange men do not get an opportunity to glance at those parts of her body which arouse passion; and thus make her an object of desire. It is the responsibility of a woman to assume such poise and behaviour that she does not excite a man's passions. Even a glance of lust can infatuate a man and a seemingly harmless encounter eventually lead to mischief and corruption in society, destroying entire families.
In Iran, during the rule of the Shah when the law of Hijab had been revoked, the cases of fornication increased sharply. Every day tens of cases related to sexual crimes were heard in the courts of law. Every month tens of married mothers used to forsake their homes to enter into a perverse life of illicit sex. Five thousand of such parents established a new township outside the city of Tehran.
The condition steadily deteriorated and come to a stage that every day approximately seven infants were found abandoned in the streets of Tehran, as reported by the commissioner. It is obvious that illicit children born as a result of Fornication, whose parentage is not established, cannot create a position for themselves and are a burden to society.
Due to the absence of Hijab, adultery and fornication became common and thousands of chaste women become immoral. One of the highly effective ways of protecting the society from the sin of adultery is that women wear hijab and ward off the evil glances of sensuous men.