وَحَدَّثَنِي مَالِكٌ، أَنَّهُ بَلَغَهُ أَنَّ عَبْدَ اللَّهِ بْنَ مَسْعُودٍ، كَانَ يَقُولُ لاَ يَزَالُ الْعَبْدُ يَكْذِبُ وَتُنْكَتُ فِي قَلْبِهِ نُكْتَةٌ سَوْدَاءُ حَتَّى يَسْوَدَّ قَلْبُهُ كُلُّهُ فَيُكْتَبَ عِنْدَ اللَّهِ مِنَ الْكَاذِبِينَ ‏.‏

Malik related to me that he heard that Abdullah ibn Masud used tosay, "The slave continues to lie and a black spot grows in his heartuntil all his heart becomes black. Then he is written, in Allah'ssight, among the liars." Translation Not Available

Book reference: Muwatta Imam Malik Book 56 Hadith 1831
Web reference: Muwatta Imam Malik Book 56 Hadith 18