They inherited wealth from their father and invested it in some business; how should they pay zakaah?

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Check below answers in case you are looking for other related questions:
Is zakaah due on manufacturing equipment?
Each partner must pay zakaah on his share of the profits from mudaarabah (partnership)

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Related Answers:
Detailed discussion of zakaah on shares
His father gave him something then he died before the son took it
Can he give to one of his children and not the others if he is poor?
Is zakaah due on manufacturing equipment?
Each partner must pay zakaah on his share of the profits from mudaarabah (partnership)

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