[Machine] Allah ﷺ prohibited the meat of domestic donkeys at the time of Khaybar. The judge Ibn 'Amr used to say that the Messenger of Allah ﷺ prohibited it, but Ibn 'Abbas disagreed. He recited the verse, "Say, 'I do not find within that which was revealed to me [anything] forbidden to one who would eat it unless it be a dead animal or blood spilled out or the flesh of swine'" [Surah Al-An'am, 6:145]. The people of Jahiliyah used to leave certain things out of cleanliness, so Allah revealed His book and clarified what is lawful and what is prohibited. Whatever is permitted is lawful, and whatever is prohibited is forbidden, and whatever is not mentioned is pardoned. Then Allah recited this verse, "Say, 'I do not find within that which was revealed to me [anything] forbidden to one who would eat it unless it be a dead animal or blood spilled out or the flesh of swine'" [Surah Al-An'am, 6:145]. Imam Bukhari reported the beginning of this in his Sahih, narrated by Ali bin Al-Madinini from Sufyan. If Ibn Abbas knew that the Prophet ﷺ had prohibited it categorically, he would not have allowed it for anyone else except himself, but he did not know.  

اللهِ ﷺ نَهَى عَنْ لُحُومِ الْحُمُرِ الْأَهْلِيَّةِ زَمَنَ خَيْبَرَ قَالَ قَدْ كَانَ يَقُولُ ذَلِكَ الْحَكَمُ بْنُ عَمْرٍو عَنْ رَسُولِ اللهِ ﷺ وَلَكِنْ أَبَى ذَلِكَ الْبَحْرُ يَعْنِي ابْنَ عَبَّاسٍ وَقَرَأَ {قُلْ لَا أَجِدُ فِي مَا أُوحِيَ إِلِيَّ مُحَرَّمًا} [الأنعام 145] الْآيَةَ وَقَدْ كَانَ أَهْلُ الْجَاهِلِيَّةِ يَتْرُكُونَ أَشْيَاءَ تَقَذُّرًا فَأَنْزَلَ اللهُ تَعَالَى كِتَابَهُ وَبَيَّنَ حَلَالَهُ وَحَرَامَهُ فَمَا أَحَلَّ فَهُوَ حَلَالٌ وَمَا حَرَّمَ فَهُوَ حَرَامٌ وَمَا سَكَتَ عَنْهُ فَهُوَ عَفْوٌ ثُمَّ تَلَا هَذِهِ الْآيَةَ {قُلْ لَا أَجِدُ فِي مَا أُوحِيَ إِلِيَّ مُحَرَّمًا عَلَى طَاعِمٍ يَطْعَمُهُ إِلَّا أَنْ يَكُونَ مَيْتَةً أَوْ دَمًا مَسْفُوحًا أَوْ لَحْمَ خِنْزِيرٍ} [الأنعام 145] فَقَدْ أَخْرَجَ الْبُخَارِيُّ أَوَّلَهُ فِي الصَّحِيحِ عَنْ عَلِيِّ بْنِ الْمَدِينِيِّ عَنْ سُفْيَانَ وَلَوْ عَلِمَ ابْنُ عَبَّاسٍ ؓ أَنَّ النَّبِيَّ ﷺ حَرَّمَهُ تَحْرِيمًا لَمْ يَصِرْ إِلَى غَيْرِهِ إِلَّا أَنَّهُ لَمْ يَعْلَمْهُ