Inappropriate Staring at the Opposite Gender
The basis for the prohibition of staring at the opposite gender inappropriately is the pasuk "ולא תתורו אחרי לבבכם ואחרי עיניכם אשר אתם זונים אחריהם. למען תזכרו ועשיתם את כל מצותי והייתם קדושים לאלהיכם" Chazal understand it to mean that one's eyes shouldn't gaze at inappropriately dressed women because it leads to sin.
Staring at a Woman
- It is permitted to stare at one's wife even when she's a Niddah even if it brings one's pleasure (nonetheless, it in some contexts it is still totally inappropriate). Nonetheless one may not look at certain parts of one's wife.
- It is forbidden to stare at any part of a woman's body, even her pinky, if one intends to derive pleasure from looking at it.
- For purposes of marriage, it is permitted and proper to look at one's intended wife before marrying her.