Abdullah bin Dinar says: I heard Abdullah bin Umar (may Allah be pleased with them) being asked about "Kanz" (hoarded wealth), so he replied: It is that wealth on which you do not pay Zakat.
Hadith Referenceمسند الإمام الشافعي / كتاب الزكاة / 684
Hadith Takhrijصحیح اخرجه البيهقى 4 / 83 ۔ وفى المعرفة السنن والآثار له (2213)۔
It is narrated from Nafi' (may Allah have mercy on him) that Abdullah bin Umar (may Allah be pleased with them both) used to say: Every wealth from which you pay zakat is not a treasure, even if it is buried, and every wealth from which you do not pay zakat is a treasure, even if it is not buried.
Hadith Referenceمسند الإمام الشافعي / كتاب الزكاة / 685
Hadith Takhrijصحیح موقوفا : اخرجه البيهقى فى المعرفة السنن والآثار (2212) ۔ وفي الكبرى له : 4/ 83 ۔ وعبدالرزاق (1840) ، (1841) ، (1842) وابن ابي شيبة (10519)۔