of commercial papers freed merchants from the need to carry cash everywhere and also made their journeys safer. The caliph too used the sakk to pay salaries or reward poets and minstrels. Although it was customary for merchants to set up family businesses or employ slaves to run their affairs, formal business arrangements ( muzarba ) were also common in which sleeping partners entrusted capital to travelling merchants and shared profits and losses in an agreed proportion. Islam did not stop people from making money so long as certain prohibitions were respected.
For instance, interest-bearing transactions ( riba ) were unlawful, although people circumvented usury in ingenious ways ( hiyal ), such as borrowing money in one type of coin and paying in another while disguising the interest as a commission on currency exchange (the origin of the bill of exchange). Many tales from the Thousand and One Nights (Alf Layla wa Layla) give us a picture of medieval Islamic society, featuring characters such as sailors, slaves, merchants and money-changers.