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]

  1. 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).Cite error: Closing </ref> missing for <ref> tag

Sources

  1. Bamidbar 15:39
  2. Sifrei Bamidbar 115, Nedarim 20a