Sahih Bukhari | Volume 6 | Hadith Number 439

Narrated by 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).