Casting Evil glances is clearly forbidden by the (نص قطعی) clear and explicit text of the Qur’aan. Allah Ta’ala says:

قل للمومنین یغضوا من ابصارھم

“O Nabi (صلی اللہ علیہ وسلم) Tell the believing men to lower their gazes.”
(Sura Nur ; Ayat 30, Juz 18)

(Meaning, don’t look at ghair mahram women and handsome boys). Therefore he who casts evil glances, is opposing the clear and explicit command of Qur’aan, and one who opposes the clear and explicit command of Qur’aan is guilty of committing a HARAAM act. Thus, to save oneself from this sin, it is sufficient to meditate upon the fact that the one who casts evil glances is opposing a commandment of the Qur’aan. In other words, he is disobeying Allah Ta’ala.

Source: The 14 Harms Of Casting Evil Glances