Musnad Ahmad 2:1

'Abd al-Rahman ibn Mahdi narrated to us, from Sufyan, from Abu Ishaq, from Harithah, who said: Some people from the people of al-Sham came to 'Umar and said: "We have acquired wealth, horses, and slaves, and we would like there to be Zakat and purification for us in them." He said: "My two companions before me did not do it, so I shall not do it." Then he consulted the companions of Muhammad, may Allah bless him and grant him peace, among whom was 'Ali. 'Ali said: "It is good, provided it is not a fixed tribute (jizyah) that they are held to after you."