And tell the believing women to lower their gaze and guard their private parts from sin and not show of their adornment except only that which is apparent, and draw their headcovers over their necks and bosoms and not reveal their adornment except to their husbands, their fathers, their husbands' fathers, their sons, their husbands' sons, their brothers, or their brothers' sons, or their sisters' sons, or their women (i.e., their sisters in Islam), or their female slaves whom their right hands possess, or old male servants free of physical desires, or small children who have no sense of women's nakedness. And let them not stamp their feet so as to reveal what they hide of their adornment. And turn unto Allah altogether, O you Believers, in order that you may attain success.
(An-Nur, 24:31)

"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!"
HOLY QUR'AN 7:2