Tafsir of Al-Mutaffifeen 83:10

{Those who deny} This is a description used for condemnation, not for mere explanation. It is like saying, "So-and-so, the corrupt and wicked, did such-and-such."

{Nay!} A rebuke to the sinful transgressor regarding his statement.

{A stain (ran) has covered their hearts} It has settled upon them just as rust settles, overcoming them. This occurs when one persists in major sins and delays repentance until a seal is placed upon their heart, such that it neither accepts goodness nor inclines toward it.

Al-Hasan said: "It is sin after sin until the heart turns black." It is said: Rāna ‘alayhi al-dhanb (the sin stained it) and Ghāna ‘alayhi (it covered it), using the terms rayn and ghayn. Al-Ghayn refers to clouds. It is also said: Rāna fīhi al-nawm (sleep settled into him), and Rānat bihi al-khamr (intoxication overcame him).

There are two recitations: one with the assimilation (idghām) of the 'lām' into the 'rā', and one with clear pronunciation (iẓhār); the assimilation is superior. The 'alif' is pronounced with imālah (inclination) and tafkhīm (fullness).

{Nay!} A rebuke against the acquisition (of sin) that has stained their hearts.

{Indeed, they will be, from their Lord, that Day, partitioned} Being partitioned from Him is a metaphor for their belittlement and humiliation. For, in the presence of kings, only the noble and honored are granted entry, while the lowly and despised are partitioned (barred) from them. As the poet said: When they approach the door of a proud man, they are pelted with stones, For people are either welcomed or partitioned.

Ibn ‘Abbās, Qatādah, and Ibn Abī Mulaykah said: "Partitioned from His mercy." Ibn Kaysān said: "From His honor."

{Nay! Indeed, the record of the righteous is in ‘Illiyyūn. And what can make you know what is ‘Illiyyūn? A register inscribed, which is witnessed by those brought near.}