Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh))
حَدَّثَنِي يَعْقُوبُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا هُشَيْمٌ، أَخْبَرَنَا أَبُو بِشْرٍ، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ، رضى الله عنهما {الَّذِينَ جَعَلُوا الْقُرْآنَ عِضِينَ} قَالَ هُمْ أَهْلُ الْكِتَابِ، جَزَّءُوهُ أَجْزَاءً، فَآمَنُوا بِبَعْضِهِ وَكَفَرُوا بِبَعْضِهِ.Narrated Ibn `Abbas:Those who have made their Scripture into parts are the people of the Scripture who divided it into portions and believed in a part of it and disbelieved the other
From Sahih al-Bukhari, whose reports the scholars accept as authentic.