The Statement of Allah On the Day when that (Al-Kanz—money gold and silver, etc., the Zakät of which has not been paid) will be heated in the fire of Hell, and with it will be branded their foreheads… (V.9:35)

Hadith Number 4661

setting

Narrated Khãlid bin Aslam

We went out with 'Abdullãh bin 'Umar and he said, "This (Verse) was revealed before the prescription of Zakat, and when Zakãt was prescribed, Allah made it a means of purifying one's wealth."