Benefit: By «رکاز» is meant a treasure buried in the ground whose owner cannot be identified, and there is a strong likelihood that it dates back to before the establishment of Muslim rule. One-fifth of it shall be paid to the public treasury (Bayt al-Mal), and this payment must be made immediately. It is not necessary to wait for a full year to pass. The remainder of the wealth will belong to the one who found it. In the present era, in some countries, the government’s seizure of the entire wealth is contrary to the Shariah.
Source: Commentary on Sunan Ibn Mājah by Mawlānā ‘Atā’ullāh Sājid, Page: 2510