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." (IT)
USC-MSA web (English) reference: Book 56, Hadith 18 (IT)
Arabic reference (IT): Book 56, Hadith 1831 (IT)