Musnad Ahmad 27:1988

Hashim narrated to us, Abd al-Aziz narrated to us, from Abdullah ibn Dinar, from Ibn Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, he who does not pay the Zakat of his wealth, Allah the Exalted will represent his wealth to him on the Day of Resurrection as a bald-headed serpent, having two black spots above its eyes. It will cling to him, or encircle his neck." He said: "It will say: 'I am your treasure, I am your treasure.'"