Malik said, "The position among us (in Madina) concerning goods which are being managed for trading purposes is that if a man pays zakat on his wealth, and then buys goods with it, whether cloth, slaves or something similar, and then sells them before a year has elapsed over them, he does not pay zakat on that wealth until a year elapses over it from the day he paid zakat on it. He does not have to pay zakat on any of the goods if he does not sell them for some years, and even if he keeps them for a very long time he still only has to pay zakat on them once when he sells them."
Malik said, "The position among us concerning a man who uses gold or silver to buy wheat, dates, or whatever, for trading purposes and keeps it until a year has elapsed over it and then sells it, is that he only has to pay zakat on it if and when he sells it, if the price reaches a zakatable amount. This is therefore not the same as the harvest crops that a man reaps from his land, or the dates that he harvests from his palms."
Malik said, "A man who has wealth which he invests in trade, but which does not realise a zakatable profit for him, fixes a month in the year when he takes stock of what goods he has for trading, and counts the gold and silver that he has in ready money, and if all of it comes to a zakatable amount he pays zakat on it."
Malik said, "The position is the same for muslims who trade and muslims who do not. They only have to pay zakat once in any one year, whether they trade in that year or not."
Arabic : Book 17, Hadith 599