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)۔