How bad a sin is looking at other 's awrah?

Looking at other's awrah is a sin. But specifically speaking, what is the level of intensity of this sin? What do the Qur'an and Hadith indicate about this matter? I saw somewhere that Rasulullah (S.A.W) said that the person looking at the awrah and the person showing the awrah, both are cursed. Is this a legitimate hadith? If there's any problem in my question please inform me. Thanks!