Yahya related to me from Malik from Nafi that Abdullah ibn Umarused to pay the zakat al-fitr for those slaves of his that were atWadi'l-Qura and Khaybar.Yahya related to me that Malik said,"The best that I have heard about the zakat al-fitr is that a man hasto pay for every person that he is responsible for supporting and whomhe must support. He has to pay forall his mukatabs, his mudabbars, andhis ordinary slaves, whether they are present or absent, as long asthey are muslim, and whether or not they are fortrade. However, hedoes not have to pay zakat on any of them that are not muslim."Malik said, concerning a runaway slave, "I think that his mastershould pay the zakat fo rhim whether or not he knows where he is, ifit has not been long since the slave ran away and his master hopesthat he is still alive and will return. If it has been a long timesince he ran away and his master has despaired of him returning then Ido not think that he should pay zakat for him.'Malik said,"The zakat al-fitr has to be paid by people living in the desert (i.e.nomadic people) just as it has to be paid by people living in villages(i.e. settled people), because the Messenger of Allah, may Allah blesshim and grant him peace, made the zakat al-fitr at the end of Ramadanobligatory on every muslim, whether freeman or slave, male or female."
USC-MSA web (English) reference: Book 17, Hadith 52
Arabic reference: Book 17, Hadith 628