Regarding zakat as a penalty and Hajj as trade
Question
[People] perform zakat with the notion that it is a fine, and Hajj with the notion of trade.
Answer
Although the obligation (farida) will be discharged in this way too, it is not accepted in the court of Allah Most High; moreover, this is a sign of the nearness of the Day of Resurrection.
Source: Fatawa Mahmudiyya
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