Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "All wealth whose zakah is paid is not kanz, even if it is buried in the ground; and all wealth whose zakah is not paid is kanz, even if it lies in the open."
This is not mahfuz (preserved); what is well known is from Sufyan, from Ubaydullah, from Nafi', from Ibn Umar, as mawquf (his own words).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7233