Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) that he (peace and blessings be upon him) said: "In rikaz (ancient treasure buried in the ground) there is one fifth."
Hadith Referenceالمعجم الأوسط / باب الألف / 1206
Hadith Takhrij«أخرجه الدارقطني فى «سننه» برقم: 3311، والطبراني فى «الكبير» برقم: 10039»