All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon Prophet Mohammad and upon all his family and companions.
Upon a person's death, their wealth immediately leaves their ownership, and the Zakat year (Hawl) on it ceases. It then enters the ownership of the heirs, who become entitled to it according to their shares prescribed in Sharia. A new Zakat year is calculated for this wealth from the moment of death. If the inheritance is divided among the heirs, each heir then calculates their Zakat year for their share, provided it reaches the Nisab (minimum threshold liable for Zakat).
As for the money that has not been divided among the heirs and remains shared, if it reaches the Nisab (85 grams of pure 24-carat gold), then Zakat is obligatory on it every year according to the Shafi'i school of thought. This is because Zakat is a right attached to the wealth, and therefore its payment is obligatory. Thus, each heir must pay Zakat on their share, upon receiving it, for all previous years (if Zakat was not already paid). This is because their ownership of this wealth has not ceased throughout the past years. Therefore, they must pay Zakat for the past years, amounting to 2.5% of it. In this regard, Al-Imam Al-Shirbini, may Allah have mercy on him, stated: "It [i.e., Zakat] is obligatory on usurped wealth if one is unable to reclaim it, and similarly for stolen, lost, or wealth fallen into the sea, or that which was buried and its location forgotten, and denied assets or debts for which there is no proof or the judge has no knowledge of, according to the more evident new opinion... Moreover, it is not obligatory to pay it until the usurped wealth and other aforementioned items are returned, due to the inability to do so beforehand. When it is returned, Zakat is paid for the past years... However, if it is only at the Nisab and there is no other wealth of its kind to cover the required amount, Zakat is not obligatory for what exceeds the first year's Hawl." [Mughni Al-Muhtaj/Vol.2/P.123]
On the other hand, the Maliki school of thought holds that for shared inherited wealth what matters is possession (Qabd) and the passing of a full year (Hawl). Therefore, there is no Zakat on inherited wealth for the years that passed before it was taken into possession. When it is taken into possession, a new Zakat year begins for it. Al-Imam Ad-Dusuqi, may Allah have mercy on him, stated: "There is no Zakat on a specific asset that was inherited and remained for years if one was unaware of it." Ad-Dusuqi commented: "The gist of what is in Al-Mudawwanah is that there is no Zakat on that asset except when it is taken into possession; when it is possessed, a new Hawl (year) begins for it, and there is no Zakat for the past years, even if it was held and one was aware of it. The implication of the author [referring to the compiler of Al-Mudawwanah] is that if it was held and one was aware of it, then it is subject to Zakat for the past years. However, the relied-upon opinion of the Mudawwanah is the consideration of possession only for the obligation." [Hashiyat Ad-Dusuqi Ala Ash-Sharh Al-Kabir/Vol. 1/P.458].
In conclusion, if any of the heirs wishes to take the more cautious approach by following the Shafi'i school of thought and pay Zakat for all the previous years, they are permitted to do so. However, if they prefer to follow the Maliki school of thought and begin calculating the Zakat year from the day they take possession of their shares of the inheritance, due to the long period the money was held, there is no blame upon them. And Allah The Almighty Knows Best.
