He took some money unlawfully. How should he repent?

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Check below answers in case you are looking for other related questions:
Cheating at work to get extra travel expenses
Her husband built an apartment in her mother’s house and her mother refused to put it in his name

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Related Answers:
He took some property from a villa that was confiscated by the state; how should the wealth be returned?
He was sent overseas to study and they gave him a complete salary by mistake
Ruling on working for or buying magazines whose content is mostly haraam, as is the case with many women’s magazines, both Arabic and western
Cheating at work to get extra travel expenses
Her husband built an apartment in her mother’s house and her mother refused to put it in his name

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