What are the conditions for writing/stipulating an object in a contract where payment is deferred (Kitabah)?

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The writing contract is permissible for any object valid for a forward sale (Salaf/Sulam). This is because the object is a defined obligation in the debt against an agreed consideration, analogous to the Salaf contract. If the object is currency, and the locale has a single prevailing currency, stating the currency generally is permissible as it defaults to the commonly used one, similar to a sale. If one currency is overwhelmingly dominant, general mention also suffices, referring to that dominant currency. However, if multiple currencies are in use and equal in prevalence, the currency must be specified by its genus and distinguishing markers. If the object is not currency, it must be described with the specifications required in a Salaf contract.