What is the ruling if the custodian mixes the deposit with his own property or the property of another?
General Chapter
Al-Mughni
Book of Deposits
Primary text
If the custodian mixes the deposit with property such that it cannot be distinguished from his own or another's property, he is liable for it, whether mixed with similar items, lesser items, or superior items of the same or different kinds (e.g., mixing dinars with dinars, or oil with oil). This is the position of al-Shafi'i and the Ashab al-Ra'y. The rationale is that by mixing it in an indistinguishable manner, he has forfeited his ability to return the specific item, thus incurring liability, similar to throwing it into the sea.
Supporting text
Ibn al-Qasim held that if dinars are mixed with dinars in a manner considered secure (wajh al-hirz), there is no liability. A narration from Malik suggests no liability unless the mixed item is inferior, as he cannot return it without diminution. However, if the owner commands the mixing, the custodian bears no liability as he acted as the owner's deputy.