Art. 904
Every person who became unjustly enriched without legal cause through another's property or at another's expense shall return the benefit. This obligation is born especially in the cases of an undue performance, a performance for a cause which did not ensued or lapsed or for an illegal or immoral performance. The contractual recognition that a debt exist or does not exist equals to a performance.
Art. 905
The claim for an undue performance is barred, of the recipient of the performance proves that the person who performed know that the debt did not exist.
Art. 907
A performance for an immoral cause may not be claimed, if the immoral cause was also related to the party who performed.
Art. 908 - Limits of liability
The recipient is obliged to return the thing received or the consideration he received for the thing. The recipient is also obliged to return the fruits and everything collected from the thing.
Art. 909
The obligation to return is extinguished if the recipient is no more enriched when the claim was served.
(Translation by Maria Canellopoulou Botti, Lecturer, Ionian University, Corfu, Greece)