Taʿyin means the actual countervalues have been specifically identified in the sale, while nasiʾa creates a future-delivery obligation where prompt exchange is required.
The fact that a non-monetary ribawi item need not always be physically carried away before the parties leave does not legalize a deferred commodity debt. Specifying actual existing heaps now differs from promising to provide the barley a month later.
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Riba: Operative Causes, Unequal Exchange and Deferral
Taʿyin means the actual countervalues have been specifically identified in the sale, while nasiʾa creates a future-delivery obligation where prompt exchange is required.
The fact that a non-monetary ribawi item need not always be physically carried away before the parties leave does not legalize a deferred commodity debt. Specifying actual existing heaps now differs from promising to provide the barley a month later.