Zakat (Kitab Al-Zakat)
Dawud :: Book 9 : Hadith 1569
Narrated Ali ibn AbuTalib:
The Prophet (peace_be_upon_him) said: I have given exemption regarding horses and slaves; with regard to coins, however, you must pay a dirham for every forty (dirhams), but nothing is payable on one hundred and ninety. When the total reaches two hundred, five dirhams are payable.