What is the ruling regarding mixing sound currency with counterfeit currency in a trust?

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If the custodian mixes sound currency with counterfeit currency, or mixes sound currency with previously mixed currency, liability does not attach. This is because the currencies remain distinguishable, meaning the custodian can still return the sound currency to the owner without hindrance, similar to leaving the trust property in a chest containing personal bags. This view is held by Al-Shafi'i and Malik, and no known disagreement exists on this point. The same ruling applies if dirhams are mixed with dinars, or white coins with black ones.