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bukhari:4227Muḥammad b. Abū al-Ḥusayn > ʿUmar b. Ḥafṣ from my father > ʿĀṣim > ʿĀmir > Ibn ʿAbbās

I do not know whether the Prophet ﷺ forbade the eating of donkey-meat (temporarily) because they were the beasts of burden for the people, and he disliked that their means of transportation should be lost, or he forbade it on the day of Khaibar permanently.  

البخاري:٤٢٢٧حَدَّثَنِي مُحَمَّدُ بْنُ أَبِي الْحُسَيْنِ حَدَّثَنَا عُمَرُ بْنُ حَفْصٍ حَدَّثَنَا أَبِي عَنْ عَاصِمٍ عَنْ عَامِرٍ عَنِ ابْنِ عَبَّاسٍ ؓ قَالَ

لاَ أَدْرِي أَنَهَى عَنْهُ رَسُولُ اللَّهِ ﷺ مِنْ أَجْلِ أَنَّهُ كَانَ حَمُولَةَ النَّاسِ فَكَرِهَ أَنْ تَذْهَبَ حَمُولَتُهُمْ أَوْ حَرَّمَهُ فِي يَوْمِ خَيْبَرَ لَحْمَ الْحُمُرِ الأَهْلِيَّةِ  


See similar narrations below:

Collected by Muslim, Bayhaqī
muslim:1939Aḥmad b. Yūsuf al-Azdī > ʿUmar b. Ḥafṣ b. Ghiyāth from my father > ʿĀṣim > ʿĀmir > Ibn ʿAbbās

I do not know whether Messenger of Allah ﷺ prohibited (the eating of the domestic ass) due to the fact that they were the beasts of burden for the people, so he (the Holy Prophet) did not like their beasts of burden to be destroyed (as a matter of expediency), or he prohibited the use of the flesh of domestic asses (not as an expediency but as a law of the Shari'ah) on the Day of Khaibar.  

مسلم:١٩٣٩وَحَدَّثَنِي أَحْمَدُ بْنُ يُوسُفَ الأَزْدِيُّ حَدَّثَنَا عُمَرُ بْنُ حَفْصِ بْنِ غِيَاثٍ حَدَّثَنَا أَبِي عَنْ عَاصِمٍ عَنْ عَامِرٍ عَنِ ابْنِ عَبَّاسٍ قَالَ

لاَ أَدْرِي إِنَّمَا نَهَى عَنْهُ رَسُولُ اللَّهِ ﷺ مِنْ أَجْلِ أَنَّهُ كَانَ حَمُولَةَ النَّاسِ فَكَرِهَ أَنْ تَذْهَبَ حَمُولَتُهُمْ أَوْ حَرَّمَهُ فِي يَوْمِ خَيْبَرَ لُحُومَ الْحُمُرِ الأَهْلِيَّةِ  

bayhaqi:19460Abū Ṭāhir al-Faqīh > Abū Bakr Muḥammad b. al-Ḥusayn al-Qaṭṭān > Aḥmad b. Yūsuf > ʿUmar b. Ḥafṣ b. Ghiyāth from my father > ʿĀṣim > ʿĀmir > Ibn ʿAbbās

[Machine] I do not know why the Messenger of Allah, ﷺ , prohibited it. Perhaps it was because it was burdensome for the people, so he disliked their burdens being taken away or prohibited them from eating the flesh of domesticated donkeys on the day of Khaybar.  

البيهقي:١٩٤٦٠وَقَدْ أَخْبَرَنَا أَبُو طَاهِرٍ الْفَقِيهُ أنبأ أَبُو بَكْرٍ مُحَمَّدُ بْنُ الْحُسَيْنِ الْقَطَّانُ ثنا أَحْمَدُ بْنُ يُوسُفَ ثنا عُمَرُ بْنُ حَفْصِ بْنِ غِيَاثٍ حَدَّثَنِي أَبِي عَنْ عَاصِمٍ عَنْ عَامِرٍ عَنِ ابْنِ عَبَّاسٍ ؓ قَالَ

لَا أَدْرِي أَنَهَى عَنْهُ رَسُولُ اللهِ ﷺ مِنْ أَجْلِ أَنَّهُ كَانَ حَمُولَةَ النَّاسِ فَكَرِهَ أَنْ تَذْهَبَ حَمُولَتُهُمْ أَوْ حَرَّمَهُ فِي يَوْمِ خَيْبَرَ لَحْمَ الْحُمُرِ الْأَهْلِيَّةِ  

رَوَاهُ الْبُخَارِيُّ فِي الصَّحِيحِ عَنْ مُحَمَّدِ بْنِ أَبِي الْحُسَيْنِ عَنْ عُمَرَ بْنِ حَفْصٍ وَرَوَاهُ مُسْلِمٌ عَنْ أَحْمَدَ بْنِ يُوسُفَ الْأَزْدِيِّ