Looking at the parts of the body that must be covered is forbidden and falls under Allah’s words:

“Say, ‘My Lord has only forbidden indecencies’”

and His words:

“Do not approach indecencies.”

Although “indecencies” most obviously refers to vaginal or anal intercourse and the associated acts of touching, looking, and so forth—as in the account of Lot:

“Do you commit an indecency such as no one in all the worlds has committed before you?”

“Do you commit indecency while you can see?”

and His words:

“Do not approach unlawful sexual intercourse. Indeed, it is an indecency”—

the term “indecency” also includes uncovering the parts of the body that must be covered, even without sexual contact. Thus Allah says:

“When they commit an indecency, they say, ‘We found our fathers doing it.’”

This indecency was their practice of circumambulating the House naked. They used to say, “We will not circumambulate in clothes in which we have disobeyed Allah.” The Hums, however, circumambulated in their clothes. Anyone else who obtained clothes from the Hums circumambulated in them; otherwise, he circumambulated naked. If he circumambulated in his own clothes, they became forbidden to him, so he discarded them. They were therefore called liqāʾ (discarded garments).

Likewise, if a woman could not obtain clothes, she placed one hand over her genitals and the other over her anus and circumambulated, saying:

“Today some of it, or all, is bare;
Whatever shows, I do not permit.”

Allah called this an indecency. His words in this context:

“Say, ‘My Lord has only forbidden indecencies, whether open or hidden’”

also encompass uncovering and displaying the parts of the body that must be covered. This is further confirmed by the fact that describing the sexual act in explicit language is called obscenity and obscene speech. Exposing the intimate parts and the act to sight is therefore like exposing them to hearing.