وإن كانت كاسدة لم يجز البيع بها حتى يعينها
Translation: If the fulus are obsolete, a sale using them is invalid until the coins are specified.
Kasid coins no longer function as accepted money; they are treated as identifiable items of property. Merely promising unspecified obsolete pieces does not adequately identify the consideration.
Once particular items are identified and the other sale conditions hold, they may be exchanged as property rather than assumed to be circulating currency.
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Why obsolete fulus require identification
Bab al-Sarf: Circulating Fulus, Obsolete Coins and Money-Changer Exchanges
وإن كانت كاسدة لم يجز البيع بها حتى يعينها
Translation: If the fulus are obsolete, a sale using them is invalid until the coins are specified.
Kasid coins no longer function as accepted money; they are treated as identifiable items of property. Merely promising unspecified obsolete pieces does not adequately identify the consideration.
Once particular items are identified and the other sale conditions hold, they may be exchanged as property rather than assumed to be circulating currency.