Yahya related to me from Malik that he had heard that Umar ibnAbd al-Aziz wrote to his governor in Damascus about zakat saying,"Zakat is paid on the produce of ploughed land, on gold and silver,and on livestock."Malik said, "Zakat is only paid on threethings:
the produce of ploughed land, gold and silver, and livestock."
USC-MSA web (English) reference: Book 17, Hadith 3
Arabic reference: Book 17, Hadith 583