Islam forbids looking at a member of the opposite sex with desire; for the eye is the key to the feelings, and the look is the messenger of desire, carrying the message of fornication or adultery.
A poet of ancient times has said:
'All affairs begin with the sight,
the raging fire a spark can ignite'
While a contemporary poet declares:
'A look, then a smile,
then a nod of the head,
then a talk, then a promise,
then the warmth of the bed'
Source: Madrassah Inaamiyah