Sahih Bukhari Volume 009, Book 089, Hadith Number 286.
Narrated By Abu Humaid Al-Sa'idi : The Prophet appointed a man from the tribe of Bani Asad, called Ibn Al-Utabiyya to collect the Zakat. When he returned (with the money) he said (to the Prophet), "This is for you and this has been given to me as a gift." The Prophet stood up on the pulpit (Sufyan said he ascended the pulpit), and after glorifying and praising Allah, he said, "What is wrong with the employee whom we send (to collect Zakat from the public) that he returns to say, 'This is for you and that is for me?' Why didn't he stay at his father's and mother's house to see whether he will be given gifts or not? By Him in Whose Hand my life is, whoever takes anything illegally will bring it on the Day of Resurrection by carrying it over his neck: if it is a camel, it will be grunting: if it is a cow, it will be mooing: and if it is a sheep it will be bleating!" The Prophet then raised both his hands till we saw the whiteness of his armpits (and he said), "No doubt! Haven't I conveyed Allah's Message?" And he repeated it three times.