Musnad Ahmad 792:5

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Bahz ibn Hakim, from his father, from his grandfather, that he heard the Prophet, peace and blessings of Allah be upon him, saying: "Whoever is asked by his client for the surplus of his wealth and he does not give it to him, it will be made into a bald-headed poisonous snake on the Day of Resurrection."