Abdullah ibn Hind reported: Ali, may Allah be pleased with him, said, “Verily, faith begins like a fragment of white in the heart. Each time faith increases in magnitude, it increases that brightness. When he completes his faith, the entire heart is brightened. Verily, hypocrisy begins like a fragment in the heart. Each time hypocrisy increases in magnitude, it increases that darkness. When he completes his hypocrisy, the entire heart is darkened. I swear by Allah, if you were to split open the heart of a believer, you would find brightness and if you were to split open the heart of a hypocrite, you would find darkness.”
Source: Shu’ab al-Imān 37
عَنْ عَبْدِ اللهِ بْنِ عَمْرِو بْنِ هِنْدَ قَالَ قَالَ عَلِيٌّ رَضِيَ اللهُ عَنْهُ إِنَّ الْإِيمَانَ يَبْدُو لُمْظَةً بَيْضَاءَ فِي الْقَلْبِ فَكُلَّمَا ازْدَادَ الْإِيمَانُ عِظَمًا ازْدَادَ ذَلِكَ الْبَيَاضُ فَإِذَا اسْتَكْمَلَ الْإِيمَانَ ابْيَضَّ الْقَلْبُ كُلُّهُ وَإِنَّ النِّفَاقَ يَبْدُو لُمْظَةً فِي الْقَلْبِ فَكُلَّمَا ازْدَادَ النِّفَاقُ عِظَمًا ازْدَادَ ذَلِكَ سَوَادًا فَإِذَا اسْتَكْمَلَ النِّفَاقَ اسْوَدَّ الْقَلْبُ كُلُّهُ وَايْمُ اللهِ لَوْ شَقَقْتُمْ عَنْ قَلْبِ مُؤْمِنٍ لَوَجَدْتُمُوهُ أَبْيَضَ وَلَوْ شَقَقْتُمْ عَنْ قَلْبِ مُنَافِقٍ لَوَجَدْتُمُوهُ أَسْوَدَ
37 شعب الإيمان