Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.062A.

Zakah collectors are officials appointed by the leader or his deputy to collect it from the rich. Among them are the custodians of zakah, shepherds and clerks for its administration. They must be Muslims and should consist of those who are potentially not eligible for zakah. This includes the family of the Prophet–that is, Banu ‘Abdul Mutallib. It is related by al-Muttalib ibn Rabi’ah ibn Harith ibn ‘Abdul Muttalib that he and al-Fadl ibn al-‘Abbas went to the Messenger of Allah, upon whom be peace: “One of us said: ‘O Messenger of Allah! We have come to you so that you may invest us with authority to administer zakah, that we shall gather (collect) the benefits the people are to receive, and render service to you that others give.’ The Messenger of Allah answered: ‘Indeed, zakah ought not to be given to Muhammad or to the family of Muhammad. Zakah is nothing but filth that comes out from people’s properties.'” This is reported by Ahmad and Muslim. Another version states: “It is not permitted to Muhammad or to the family of Muhammad.”