Musnad Ahmad 27:1749

Musa ibn Dawud narrated to us, Abd al-Aziz ibn Abd Allah narrated to us, from Abd Allah ibn Dinar, from Abd Allah 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, it will be represented to him on the Day of Resurrection as a bald-headed serpent with two black spots. It will cling to him," or he said, "It will encircle his neck." He said: "It will say to him: 'I am your treasure, I am your treasure.'"