Maliks Muwatta Book 17, Hadith Number 39.
Section : The Zakat on Slaves, Horses and Honey.
Yahya related to me from Malik from Ibn Shihab from Sulayman ibn Yasar that the people of Syria said to Abu Ubayda ibn al-Jarrah, “Take zakat from our horses and slaves,” and he refused. Then he wrote to Umar ibn al-Khattab and he (also) refused. Again they talked to him and again he wrote to Umar, and Umar wrote back to him saying, “If they want, take it from them and (then) give it back to them and give their slaves provision.”
Malik said, “What he means, may Allah have mercy upon him, by the words ‘and give it back to them’ is, ‘to their poor.'”