Аль-Мутаффифин 83:14

sins has destroyed their innate capacity to distinguish right from wrong. Sayyidna Abu Hurairah ؓ narrates that the Holy Prophet ﷺ said: "Surely, when the servant commits a sin, a black dot appears on his heart. If he repents from it, his heart is polished clean. However, if he increases in the sin, the blackness continues to increase. That is the statement of Allah: كَلَّا ۖ بَلْ ۜ رَانَ عَلَىٰ قُلُوبِهِم 'No! But that which they used to commit has covered their hearts with rust. [ 83:14] '." [ Baghawi, Ahmad, Tirmidhi, Nasai, Ibn Majah, Ibn Hibban and al-Hakim have recorded it, and Tirmidhi has rated it as sahih, as quoted by Mazhari ]. The particle kalla كَلَّا ، in Arabic grammar, is called harf-ur-ra’ d` 'particle of disapproval, particle of repelling or averting'. In the preceding verses, mention was made of the attitude of the unbelievers towards the Qur'anic verses, in that when they are recited to them, they say, " (These are) tales of the ancients." [ 13]. The present verse uses kalla كَلَّا to repel the false idea of the ignoramus [ that Qur'an is the tale of the ancients ]. In fact, [ the heavy ] load of their sins have eclipsed the light and innate capacity to separate the right and the wrong. This capacity is innate and inborn in man. The verse purports to say that their rejection is not based on any logical or intellectual evidence, but their hearts have become blind, as a result they are unable to see the good and the bad.