From a shari’a perspective, riba has a number of characteristics that set it apart from legitimate sources of income. Accordingly, any source of income in which one or more of the following explicitly or implicitly do exist will be, or be tantamount to, riba:

• Paying back an extra addition over principal or capital, whether in a tangible (additional amount) or intangible form (postponement of a countervalue, non-monetary benefit or favor, etc). This extra addition should be based on a promise or condition indicated in the contract (or even inferred from norms or customs). This is derived from the general implication of the following hadith (prophetic tradition): “every loan that attracts or brings about a benefit is riba” (though it is weak or dha’eef, this hadith is authenticated based on ijma’a). An example would be a service rendered by the debtor to the creditor in conjunction with the loan (qard).
• The payment of an extra addition over principal or capital where both the addition and capital are guaranteed. Any type of investment which guarantees capital or proceeds such as bonds, preferred stock, deposits, etc.
• The payment of an extra addition even without being stipulated in the contract in the way of promise or condition. This is the case when there is an element of understanding between the parties that would force the debtor to pay an extra amount or render a service whatsoever (this is based on the maxim “observed norms shall tantamount to explicitly indicated conditions“).