Sinfulness is mentioned in the Quran in these verses:

[2:219] They ask you about intoxicants and gambling: say, “In them there is a gross sin, and some benefits for the people. But their sinfulness far outweighs their benefit.” They also ask you what to give to charity: say, “The excess.” God thus clarifies the revelations for you, that you may reflect,

[2:220] upon this life and the Hereafter. And they ask you about the orphans: say, “Bringing them up as righteous persons is the best you can do for them. If you mix their property with yours, you shall treat them as family members.” God knows the righteous and the wicked. Had God willed, He could have imposed harsher rules upon you. God is Almighty, Most Wise.

[3:178] Let not the disbelievers think that we lead them on for their own good. We only lead them on to confirm their sinfulness. They have incurred a humiliating retribution.

To learn more, read the Quran in English.

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