It is narrated from Sayyiduna Zayd bin Arqam (may Allah be pleased with him); he said: The Messenger of Allah (peace and blessings be upon him) sent Sayyiduna Ali (may Allah be pleased with him) as governor over Yemen, and buried treasure (rikaz) was brought to him; he took one-fifth of it and returned the rest to its owner. This reached the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) was pleased with it.
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4974