Musnad Ahmad 30:638

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from 'Asim, from Abu Salih, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever possesses wealth and does not pay its due, it will be made for him on the Day of Resurrection a bald-headed serpent with two black spots above its eyes. It will follow him until he places his hand in its mouth, and it will continue to gnaw upon it until judgment is passed between the servants."