Khalid bin Aslam, the freed slave of 'Umar bin Khattab, said: "I went out with 'Abdullah bin 'Umar, and a Bedouin met him and recited to him the words of Allah: 'And those who hoard up gold and silver (the money, the Zakah of which has not been paid) and spend them not in the way of Allah . Ibn 'Umar said to him.
'The one who hoards it and doe; not pay the Zakat due on it, woe to him. But this was before the (ruling on) Zakat was revealed.
When it was revealed, Allah made It a purification of wealth' Then he turned away and said: ;I do not mind if I have (the equivalent of) Uhud in gold provided that I know how much it is and I pay Zakat on it and I ils.e it in obedience of Allah, the Mighty and Sublime.'" (Sahih)