Is it permissible to spend counterfeit or debased currency (ghish)?

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The preferred ruling is permissibility for spending debased currency if the people have mutually agreed upon it, similar to agreed-upon fiduciary money (fulus). This view is narrated from [Ahmad] concerning dirhams called Musaybiyyah, which were mostly copper with some silver, where he permitted it if it was an agreed-upon standard. The justification for permissibility lies in the fact that the components are known, there is no deception (gharar), and its widespread use across generations without objection suggests tolerance, avoiding undue hardship and harm. Furthermore, its purpose is clear and observable, unlike jeweler's dust. The prohibition is thus understood to apply only when the adulteration is hidden, leading to deception, which is the core evil prohibited by the Prophet's saying, "Whoever deceives us is not of us."