In the development history, has experienced the evolution of money before becoming a medium of exchange like the current modern. Before man discovered a metal that can be used as a medium of exchange, they have used goods and even livestock as a medium of exchange that serves as money and called a commodity money. But when the precious metals and stones found, they began to exchange by using precious metals, especially gold and silver. Precious metals, printed by the authorities into fragments with a certain weight, as legal tender.

In the Qur'an and the hadith, gold and silver has been mentioned both in its function as a currency or as a symbol of wealth and riches are stored. This can be seen in QS. At-Tauba: 34 which describes the people who hoard gold and silver, either in the form of currency or in the form of common wealth and they do not want to spend Zakah will be threatened with a painful punishment. This verse also stresses the obligation of Zakah for precious metals in particular. In Sura al-Kahf: 19 God tells the story of Ash-Habul Kahf (cave dwellers) who sent one of their friends to spend the silver (wariq) to buy food after they slept 309 years of diving in the cave. The Qur'an uses the word that means wariq of silver coins or dirhams.

In addition, the Qur'an also tells the story of the Prophet Joseph was thrown into a well by his brothers and found the merchants travelers. By them, Joseph then sold at a cheap price of just a few dirhams. This verse clearly using words dirhams which means coin of silver. From the stories told by the Koran, it is clear that the use of two precious metals (bimetallism) as the currency has been done by humans thousands of years before the birth of Prophet Muhammad.

In addition, many traditions of the Prophet Muhammad who called dinars and dirhams, or use wariq said. Rasulullah SAW said, "with dinar Dinar, there is no advantage between the two (if convertible); and the dirham dirhams and no excess in between the two (if traded)." (Reported by Muslim). In another hadith the Prophet Muhammad used the word wariq as in the following hadith: "silver coins numbering five auqiyah under no obligation zakat on it." (Bukhari and Muslim).

Money Function in Islamic Economics
In every economic system, the primary function of money is always a medium of exchange (medium of exchange). From the main function is derived other functions such as money as a standard of value, store of value, unit of account and standard of deferred payment. Any other currency will undoubtedly works like this.

In a capitalist economic system, money is seen not only as legal tender (legal tender) but also seen as a commodity. Thus, according to this system, money can be traded with an excess of either on the spot as well as tough. In this perspective the money can also be leased (leasing).

In Islam, anything that serves as money, then the function only as a medium of exchange. He is not a commodity that can either dijualbelikan with an excess of on the spot or not. One important phenomenon of the characteristics of money is that it is not necessary to be consumed, it is not necessary for himself, but needed to buy other goods that human needs can be met. This is explained by Imam Ghazali that only gold and silver metal in the substance (zatnya itself) there is no benefit or purpose-tujuaannya. According to him in his book Ihya Ulumiddin "Both of them do not have anything but they mean everything". Both are like a mirror, he does not have color but she can reflect all the colors.

Even in the early days of Islam's community with terbisa bermuamalah dinar and dirham, the possibility to make other goods as a currency that serves as a medium of exchange has emerged in the minds of friends. For example Umar once said, "I want (one time) make camel as a means of exchange." This statement from the lips of a very understanding about the nature and functions of money in the economy. According to Omar, the real money as a medium of exchange should not be limited to the two precious metals like gold and silver. Both these precious metals will experience instability when the instability on the demand side and supply. Because of that, whatever, can actually serve as money, including camel leather. In his view, when an item changes its function into a medium of exchange (money) then the function will eliminate its monetary function or at least will dominate its function as a normal commodity.

Shaykh al-Islam Ibn Taymiyyah also argued that money as a medium of exchange material can be drawn from what was agreed by the prevailing custom ( 'urf), and the term created by humans. He does not have to be limited from the gold and silver. For example, the dinar and dirham term itself has no natural boundaries or shari'ah '. Dinar and the dirham is not necessary for himself but as Wasilah (medium of exchange) a medium of exchange function is not related to any purpose, not related to material that does not put them in touch with the print image, but with this function of objective human needs can be met (See, Majmuatul Fatawa).

In general, the scholars of Islam and social scientists agree on the functions of money as a medium of exchange only. Rows of renowned scholars such as Imam Ghazali, Ibn Taymiyyah, Ibn al-Qayyim al-Jawziyyah, Ar-Raghib al-Ashbahani, Ibn Khaldun, al-Al-Maqrizi and Ibn Abidin clearly pointed out the main function of money as a medium of exchange. Therefore, the currency must be fixed, its value does not rise and fall.

Paper money is commonly used today is called fiat money. So called because the ability of money to serve as a medium of exchange and have no buying power because of the money backed by gold.

Once the money is following the gold standard (gold standard). Yet this regime has been long abandoned by the world economy in the mid-decade 1930's (England, leaving in 1931 and the whole world had abandoned in 1976). Now the paper money became a medium of exchange because the government designated it a medium of exchange. If the government revoke its decision and use the money from other species, will bank notes will have no value at all.

Many people who doubt or do not even know the law in terms of paper money from the sharia. Some argue that paper money does not apply usury, so that if someone owes Rp. 100,000.00 then returned to the borrower as much as Rp. 120,000.00 within three months, then not including usury. They assume that what applies at the time of the Prophet is gold and silver money and what is forbidden to exchange with an excess of the gold and silver, because it is not paper money usury laws apply to him. The answer can we find the explanation and that the currency can be made from any object, including camel leather, Umar said. When it was established as a legitimate currency, then the stuff that changed the function of goods used to be a medium of exchange with all its derivatives functions. Jumhur scholars agree that illat in gold and silver are prohibited unless a similar exchange with a similar, equal to equal, by the Prophet Muhammad is because "tsumuniyyah", ie those goods become a medium of exchange, store of value in which all goods are weighed and judged by its value .

Because the bills are de facto and de jure has become a legitimate means of payment, though no longer backed by gold, then the position in the same legal position of the gold and silver at the time of the Koran down a legal tender. Therefore, at present usury bills. Paper money is also recognized as assets that must be removed from her charity. Legitimate Zakatpun issued in the form of paper money. Similarly, it can be used as a tool to pay the dowry.

Capital in the Islamic Perspective
Capital is in English called the capital means goods produced by natural or man-made, which is required not to satisfy human wants directly, but to help produce other goods which will be able to meet immediate human needs and generate profits (See, William N . Loucks and J. Weldon Hoot, See, William N. Loucks and J. Weldon Hoot, Comparative Economic Systems, pp. 19 Comparative Economic Systems View, William N. Loucks and J. Weldon Hoot, Comparative Economic Systems, pp. 19, pp. 19). Physically there are two types of capital is fixed capital and circulating capital. Fixed capital such as buildings, machinery or factories, ie, objects that when benefits are not enjoyed by the existence of the substance decreases. The circulating capital such as raw materials and money when the benefits enjoyed, the substance is missing. Differences both in the shari'a can be seen as follows. Fixed capital in general can be rented, but can not be loaned (qardh). While the circulation of capital that can be loaned consumptive nature (qardh) but can not be rented. This is because ijara in Islam can only be performed on objects that have characteristics, the substance can be enjoyed separately or all at once. When a rental item, then the benefits of these items are separated from the owner. He is now enjoyed by the tenant, but the ownership status remains at the owner. When the lease expired, the goods were returned to the owner in as new condition.

Money does not have such properties. When a person uses the money, the money ran out. If he uses the money from the loan, then he take on debt for the amount used and must be returned in the same amount (mitsl) rather than its substance (a'in).

Return on Capital
From the above description is obvious that capital goods are included in the permanent category such as vehicles, cars, buildings, or the ship will get a return on capital in the form of rent wages if the transaction is used ijarah. In addition, capital goods can also get a return on capital in the form of part of the income (profit) if a transaction that is used is based on the rule musharaka "An item that can be leased, then the goods may be done musharaka it." This has been done by the Muslims of the past such as in muzara'ah transactions. In this covenant the land owner provides the land to be tilled by tenants. Benefits resulting from this effort was divided in accordance with the agreement, for example 50:50.

Unlike the fixed capital, circulating capital (in this case money) will not get a return on capital in the form of wages as in ijara lease. Because Islam is not money in the commodities that can be rented or dijualbelikan with excess. He needed only as a medium of exchange. But he has a return on capital when developed in the form of mudaraba akad. He also lent (qardh) but not allowed to exceed the return anyway. Such excess into the category of riba.