Sahih al-Bukhari 4917
Sahih al-Bukhari · Book 65: Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh)) · "Cruel, and moreover base-born (of illegitimate birth) ." (V.68:13)
Narrated Ibn `Abbas:
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 .
(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).