Anas (RAA) narrated that Abu Bakr As-Siddiq (RAA) wrote him this letter, "This is the obligatory Zakah, which the Messenger of Allah (ﷺ) made obligatory for every Muslim, and which Allah, the Almighty had commanded him to observe. 'For each twenty-four camels, or less, their Zakah is to be paid as sheep; for every live camels, their Zakah is one sheep. When the amount of camels is between twenty -five to thirty- five, the due Zakah is one she-camel 'bint makhad' (a camel which is one year old and just starting the second year) or a male camel 'ibn labun'(a young male camel which is two years old and already starting the third year). However, when the amount of camels reaches thirty-six, the due Zakah is a young she-camel 'bint labun' (a young female camel, which is two years old and already starting the third year). When they reach forty six to sixty camels, their due Zakah is a she camel 'hiqqah' (which is three years old and starting the fourth). When they reach sixty-one to seventy-five, one 'Jaz'ah' (a four year old camel already starting its fifth year). When their number is between seventy-six to ninety camels, their due Zakah is two young she camels 'bint labun'. When they are in the range between ninety-one to one hundred and twenty camels, the Zakah is two young she camels 'hiqqah'. If they are over a hundred and twenty camels, on every forty camels, one 'bint labun' is due. And for every fifty camels (over one hundred and twenty) a young she-camel 'hiqqah' is due, And anyone, who has got only four camels, does not have to pay Zakah unless he (the owner of the camels) wants to give something voluntarily. Regarding the Zakah of grazing sheep, if they are between forty and one hundred and twenty, one sheep is due as Zakah. lf they are between 120 and 200, two sheep are due. If they are between 200 and 300, three sheep are due. If they exceed three hundred sheep, then one sheep is due for every extra hundred grazing heads. If the grazing sheep are less than forty, (even if they are 39) then no Zakah is due on them, unless he (the owner of the camels) wants to give something voluntarily. One should not combine (i.e. gather young animals together) or separate them for fear of paying Zakah. When there is a mixture of cattle shared between two partners, and Zakah is paid jointly between them, then they have to calculate it equally among them (depending on the share of each). Neither an old or a defective animal nor a male goat (a ram used for breeding) may be taken as Zakah, unless the Zakah collector wishes to do so. Concerning silver, the Zakah paid is a quarter of a tenth for each 200 Dirhams. If the amount of silver is less than two hundred Dirhams (even if it is 190) then no Zakah is to be paid for it, unless the owner wishes to do so. If the number of camels reaches the number on which a jaz'ah (a four year old camel already starting its fifth year) is due as Zakah, but he only has a 'hiqqah' (a she camel which is three years old and starting the fourth), it should be accepted from him along with two sheep if they were available (to compensate for the difference) or twenty Dirhams. If on the other hand he has to offer a 'hiqqah' as Zakah, but he only has a jaz'ah, it is accepted from him, and the Zakah collector will then pay him the difference, which is twenty Dirhams or two female sheep.' Related by AI-Bukhari.
English reference: Book 4, Hadith 624
Arabic reference: Book 4, Hadith 599