How can one atone for not paying the obligatory zakat on wealth?

Withholding zakat (definition) is one of the greatest major sins and a grave transgression. This is indicated by the words of Allah Almighty: "The Day it will be heated in the fire of Hell and scorched thereby will be their foreheads, their flanks, and their backs, [with the words], 'This is what you hoarded for yourselves, so taste what you used to hoard'" (Quran 9:35), and the words of the Prophet, peace and blessings be upon him: "There is no owner of gold or silver who does not pay its due right except that when the Day of Resurrection comes, plates of fire will be prepared for him..."

One must repent sincerely to Allah for this sin and hasten to pay all overdue zakat, as it is a debt and a right for the poor. If one is unable to precisely determine the exact amount due, they must strive their best and pay what they believe will absolve their responsibility. Indeed, whoever delays paying zakat has sinned and must promptly pay it for all past years.