Sunan Ibn Majah, Chapter: Chapters Regarding Funerals

"We went out with the Messenger of Allah (saw) to attend a funeral, and he saw some people who had cast aside their upper sheets and were walking in their shirts only. The Messenger of Allah (saw) said: 'Are you adopting the practice of the days of ignorance?' or; 'Are you imitating the behaviour of the days of ignorance? I was about to supplicate against you that you would return in a different form.' So they put their sheets back on and never did that again." Hasan