Tafsir of Ghafir 40:19

In verse 19, it was said: يَعْلَمُ خَائِنَةَ الْأَعْيُنِ (He knows the treachery of the eyes), in other words, eyes that betray the trust. It means the action of a person who would, secretly and surreptitiously, cast a glance over something haram and impermissible for him or her, for example, casts a glance at a non-mahram person with sexual desire, and takes it away in the event someone was around, or casts a glance in a manner that is not noticed by others. All these things are open before Allah Ta’ ala.