Inappropriate Staring at the Opposite Gender

From Halachipedia

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"[1] Chazal understand it to mean that one's eyes shouldn't gaze at inappropriately dressed women because it leads to sin.[2]

Staring at a Woman

  1. 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.[3]
  2. 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).[4] Nonetheless one may not look at certain parts of one's wife.[5]
  3. For purposes of marriage, it is permitted and proper to look at one's intended wife before marrying her. [6]

Sources

  1. Bamidbar 15:39
  2. Sifrei Bamidbar 115, Nedarim 20a
  3. Brachot 24a, Rambam (Isurei Biyah 21:2), S"A EH 21:1. The Bet Shmuel 21:2 writes that it is Biblically forbidden according to the Rabbenu Yonah and rabbinically forbidden according to the Rambam. Either way, having inappropriate thoughts (Hirhur) about them is Biblically forbidden.
  4. Rambam Issurei Biyah 21:4
  5. Nedarim 20a, Raavad (Issurei Biyah 21:4)
  6. Kiddushin 41a, Rambam Ishut 3:19, S"A EH 21:3