Riyad as-Salihin

Anas (May Allah be pleased with him) said: The Messenger of Allah (ﷺ) said, "During the Mi'raj (the Night of Ascension), I saw a group of people who were scratching their chests and faces with their copper nails. I asked, 'Who are these people, O Jibril?' Jibril replied: 'These are the people who ate flesh of others (by backbiting) and trampled people's honour."'

[Abu Dawud].