Sahih al-Bukhari 4917
Narrated Ibn `Abbas:
(regarding the Verse):-- 'Cruel after all that, base-born (of illegitimate birth).' (68.13) It was revealed 
in connection with a man from Quaraish who had a notable sign (Zanamah) similar to the notable sign 
which usually-hung on the neck of a sheep (to recognize it).
حَدَّثَنَا مَحْمُودٌ، حَدَّثَنَا عُبَيْدُ اللَّهِ، عَنْ إِسْرَائِيلَ، عَنْ أَبِي حَصِينٍ، عَنْ مُجَاهِدٍ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ ‏{‏عُتُلٍّ بَعْدَ ذَلِكَ زَنِيمٍ‏}‏ قَالَ رَجُلٌ مِنْ قُرَيْشٍ لَهُ زَنَمَةٌ مِثْلُ زَنَمَةِ الشَّاةِ‏.‏