He used a credit card, which is haraam, and he owes money. Should he pay it off?

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Check below answers in case you are looking for other related questions:
The charges made by the bank when making a withdrawal when the account is empty
Entering into a partnership with a person who deals with bribes and riba

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Related Answers:
Is it permissible to delay paying the price of gold and the cost of having it made into jewellery?
Borrowing from the bank to buy a house
Is it permissible for him to inherit property that was bought with a riba-based loan?
The charges made by the bank when making a withdrawal when the account is empty
Entering into a partnership with a person who deals with bribes and riba

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