Musnad Ahmad 32:1396

Abu al-Mughirah narrated to us, Safwan narrated to us, Rashid ibn Sa'd and Abd al-Rahman ibn Jubayr narrated to me, from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When my Lord took me up [on the Night Journey], I passed by a people who had nails of copper, with which they were scratching their faces and their chests. I said: 'Who are these, O Gabriel?' He said: 'These are those who eat the flesh of people and attack their honor.'"