Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: All wealth whose zakah is paid, even if it is beneath the seven earths, is not "kanz" (hoarded treasure); and all wealth whose zakah is not paid is "kanz" (hoarded treasure), even if it lies on the surface of the earth.
This is the correct version, mawquf (the Companion's own words); Suwayd bin Abd al-Aziz, who is not strong, narrated it as marfu' (attributed to the Messenger of Allah (peace and blessings be upon him)).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7230