وَصَحَّ عَنِ ابْنِ عَبَّاسٍ عِنْدَ اَلْبُخَارِيِّ ; أَنَّهُ كَانَ عَبْدًا 1‏ .‏‏1 ‏- صحيح .‏ رواه البخاري (9 / 406 ‏- 408/ فتح)‏.‏
Translation
It has been authentically reported from Ibn 'Abbas (RA) by al-Bukhari

"...that he was a slave".