Mutable taxes are those taxes the Islamic ruler decides to impose in order to meet particular expenses of the government in exceptional cases without prior legislation by divine lawmaker hence no fixed terms for them. These taxes are called state-imposed tax. They are limited and exceptional. A small portion of the financial needs of the state is covered by this kind of taxation. They are introduced as means of crises-solving by the state. Historical instances of these taxes are the zakat imposed on commercial goods by the holy Prophet and some Caliphs as well as temporary taxation on horses during Imam Ali’s reign.
In Islamic Sharia, there are other payments obligatory or supererogatory much resembling tax but are not considered as tax because government does not collect them or law does not make them compulsory. They, however, leave impacts similar to those taxes do. Financial fines religiously due as compensation for some sins one has committed and would like to repent from (Kaffarat Mali) and self-imposed obligations to give a gift or pay alms (nudhurat) are obligatory payments. Alms (sadaqat), gifts (hibah), souvenir (hadyeh), endowment (waqf), remission of debt, and feeding the hungry (it’am) are supererogatory desirable payments considered as religious service if performed with the intention to seek Divine satisfaction.