What is the ruling on money returned by a debtor after the creditor forgave the debt without the debtor's knowledge, and is it necessary to inform the debtor of the forgiveness?

If you intend to waive a debt but do not vocalize it, you are not required to inform the debtor, and you may benefit from the returned money. However, if you vocalize the waiver but the debtor is unaware of it, there is a difference of opinion: the majority of scholars believe it is established by the offer (ijab), while the Malikis stipulate acceptance (qabul). According to the view of the majority, the amount must be returned to the debtor, and this is more cautious.