Al-Muwatta Hadith 17.7

Yahya related to me from Malik that Ibn Shihab said, "The first person to deduct zakat from allowances was Muawiya ibn Abi Sufyan." (i.e. the deduction being made automatically) . Malik said, "The agreed sunna with us is that zakat has to be paid on twenty dinars (of gold coin), in the same way as it has to be paid on two hundred dirhams (of silver)." Malik said, "There is no zakat to pay on (gold) that is clearly less than twenty dinars (in weight) but if it increases so that by the increase the amount reaches a full twenty dinars in weight then zakat has to be paid. Similarly, there is no zakat to pay on (silver) that is clearly less than two hundred dirhams (in weight), but if it increases so that by the increase the amount reaches a full two hundred dirhams in weight then zakat has to be paid. If it passes the full weight then I think there is zakat to pay, whether it be dinars or dirhams." (i.e. the zakat is assessed by the weight and not the number of the coins.) Malik said, about a man who had one hundred and sixty dirhams by weight, and the exchange rate in his town was eight dirhams to a dinar, that he did not have to pay any zakat. Zakat had only to be paid on twenty dinars of gold or two hundred dirhams. Malik said, in the case of a man who acquired five dinars from a transaction or in some other way which he then invested in trade, that, as soon as it increased to a zakatable amount and then a year elapsed, he had to pay zakat on it, even if the zakatable amount was reached one day before or one day after the passing of a year. There was then no zakat to pay on it from the day the zakat was taken until a year had elapsed over it. Malik said, in the similar case of a man who had in his possession ten dinars which he invested in trade and which reached twenty dinars by the time one year had elapsed over them, that he paid zakat on them right then and did not wait until a year had elapsed over them, (counting) from the day when they actually reached the zakatable amount. This was because a year had elapsed over the original dinars and there were now twenty of them in his possession. After that there was no zakat to pay on them from the day the zakat was paid until another year had elapsed over them. Malik said, "What we are agreed upon (here in Madina) regarding income from hiring out slaves, rent from property, and the sums received when a slave buys his freedom, is that no zakat is due on any of it, whether great or small, from the day the owner takes possession of it until a year has elapsed over it from the day when the owner takes possession of it." Malik said, in the case of gold and silver which was shared between two co-owners, that zakat was due from any one whose share reached twenty dinars of gold, or two hundred dirhams of silver, and that no zakat was due from anyone whose share fell short of this zakatable amount. If all the shares reached the zakatable amount and the shares were not equally divided, zakat was taken from each man according to the measure of his share. This applied only when the share of each man among them reached the zakatable amount, because the Messenger of Allah, may Allah bless him and grant him peace, had said, "There is no zakat to pay on less than five awaq of silver." Malik commented, "This is what I prefer most out of what I have heard about the matter." Malik said, "When a man has gold and silver dispersed among various people he must add it all up together and then take out the zakat due on the total sum ." Malik said, "No zakat is due from some one who acquires gold or silver until a year has elapsed over his acquisition from the day it became his."