Is it valid to accept a higher quality good upon a prior agreement while simultaneously demanding an extra payment (Dirham)?

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The transaction is invalid when one party agrees to deliver a superior quality good under an existing contract and then demands an additional Dirham. The basis for this ruling is that quality (*jawdah*) is merely an attribute, and attributes cannot be isolated or treated as the subject matter of a separate contract, similar to how measurable or weighed goods cannot be isolated in this manner.