Musnad Ahmad 27:1279

Hujayn ibn al-Muthanna narrated to us, 'Abd al-'Aziz ibn 'Abd Allah ibn Abi Salamah narrated to us, from 'Abd Allah ibn Dinar, from Ibn 'Umar, from the Prophet, peace and blessings of Allah be upon him, who said: "Indeed, he who does not pay the Zakat of his wealth, Allah the Almighty and Majestic will represent his wealth to him on the Day of Resurrection as a bald-headed serpent, having two black spots above its eyes. Then it will cling to him and encircle him, saying: 'I am your treasure, I am your treasure.'"