A person who acquires interests without any legal ground and prejudice to the other shall be bound to return it. The same rule shall be applied if a legal ground existed originally but disappeared subsequently.

In any of the following cases, the prestation shall not be claimed to return:
(1) If the prestation was for the performance of a moral obligation;
(2) If the prestation made by the debtor for the performance of an undue obligation;
(3) If the person who has made a prestation for the purpose of performing an obligation knew, at the time of performance, that he was not bound to perform;
(4) If the prestation was made for an unlawful cause. Except when the unlawful cause exists only with regard to the recipient.

In addition to the interests received, a recipient unjustly enriched shall return whatever he acquired by virtue of such interests. If restitution is impossible by reason of the very nature of the interests or by reason of any other circumstance, he shall be bound to reimburse the value.

The recipient, who did not know of the absence of the legal ground and the interests have no longer existed, is released from the obligation to return the interests or reimburse the value.
If the recipient knew of the absence of the legal ground at the time of the receipt, or if he was subsequently aware of it, he shall be bound to return the interests acquired at the time of the receipt or such interests still existing at the time when he was aware of the absence of the legal ground plus the interest and to make compensation for the injury, if any.

When the recipient unjustly enriched transferred gratuitously whatever he has received to a third party, and therefore the recipient is released from his obligation to return the interests, such third party shall be bound to make restitution to the extent which the recipient is released from his obligation.