Surah al-Mutaffifīn (Those Who Give Short Measure)

In the name of Allah, the Most Compassionate, the Most Merciful.

[Surah al-Mutaffifīn (83): Verse 14]
“No! Rather, their hearts have been covered with rust by what they used to earn.” (14)

He said: “It is sin after sin.” Al-Hasan said: “It is sin piled upon sin until the heart becomes blind.”

Another said: “When their sins and acts of disobedience multiplied, they enveloped their hearts.”

The underlying principle is that the heart becomes rusty through sin. As sin increases, the rust overwhelms it until it forms an encrustation. It then grows until it becomes a covering, a lock, and a seal. The heart thus becomes veiled and encased. If this happens after it has enjoyed guidance and insight, it is overturned, its top becoming its bottom. Its enemy then takes charge of it and drives it wherever he wishes. Only those whom Allah spares are spared.

He also said in Shifā’ al-‘Alīl:

As for rust, Allah Most High has said: “No! Rather, their hearts have been covered with rust by what they used to