Said by: Imam Ja'far al-Sadiq (as)
Status: ⚠️ To be checked — the meaning is widely reported from Al-Kafi, Volume 2, p. 271, but the full Arabic wording and the exact chapter and Hadith number have not been confirmed against the printed book for this draft.
Reference: Al-Kafi (Shaykh al-Kulayni), Volume 2, p. 271 (as reported) — [chapter and Hadith number — to be verified]
Arabic — core saying (excerpt):
إِذَا أَذْنَبَ الرَّجُلُ خَرَجَ فِي قَلْبِهِ نُكْتَةٌ سَوْدَاءُ، فَإِنْ تَابَ انْمَحَتْ، وَإِنْ زَادَ زَادَتْ حَتَّى تَغْلِبَ عَلَى قَلْبِهِ
English translation:
"When a man commits a sin, a black spot appears in his heart. If he repents, it is wiped away. But if he goes on sinning, the spot grows until it overcomes his whole heart, and then he can never again prosper." Another narration of the same teaching adds: in every heart there is a white spot; the black spot grows from it, and when it covers the white completely, the person no longer returns to good — as Allah says, "No! Rather, their hearts have been stained by what they used to do" (Holy Quran 83:14).
Explanation: Sin is not just an action outside us — it marks the heart. The good news is that the mark is washable: sincere repentance wipes the spot clean, as if it was never there. The warning is the other direction: sin left unrepented, again and again, darkens the heart until good advice cannot reach it. Repent early, while the heart is still soft.
Sin is not just an action outside us — it marks the heart.