Abu Dawud Book 3, Hadith Number 1569.
Chapter : Not known.
Narated By Ali ibn AbuTalib : The Prophet (PBUH) 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.