What is the status of a surplus Dinar received when settling a debt?

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If a person owes ten Dinars and pays ten by count, and the recipient finds eleven Dinars, the surplus Dinar in the receiver's possession is considered undivided property guaranteed to the original owner. This is because the receiver took possession of it as compensation for his due debt, thus making it guaranteed by that act of possession, and the owner maintains full discretion over how to deal with it.