It was narrated from Anas bin Malik that he saw the Messenger of Allah ﷺ praying on a donkey while he was riding, praying toward Khaibar with the Qiblah behind him.

Abu 'Abdur-Rahman (An-Nasa'i) said:

We do not know of anyone who reported anything to support what 'Amr bin Yahya said about praying on a donkey. As for the Hadith of Yahya bin Sa'eed from Anas, what is correct is that it is Mawquf. [1] And Allah knows best.

[1] That is a saying or action of a Companion of the Prophet ﷺ

أَخْبَرَنَا مُحَمَّدُ بْنُ مَنْصُورٍ، قَالَ حَدَّثَنَا إِسْمَاعِيلُ بْنُ عُمَرَ، قَالَ حَدَّثَنَا دَاوُدُ بْنُ قَيْسٍ، عَنْ مُحَمَّدِ بْنِ عَجْلاَنَ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّهُ رَأَى رَسُولَ اللَّهِ ﷺ يُصَلِّي عَلَى حِمَارٍ وَهُوَ رَاكِبٌ إِلَى خَيْبَرَ وَالْقِبْلَةُ خَلْفَهُ . قَالَ أَبُو عَبْدِ الرَّحْمَنِ لاَ نَعْلَمُ أَحَدًا تَابَعَ عَمْرَو بْنَ يَحْيَى عَلَى قَوْلِهِ يُصَلِّي عَلَى حِمَارٍ وَحَدِيثُ يَحْيَى بْنِ سَعِيدٍ عَنْ أَنَسٍ الصَّوَابُ مَوْقُوفٌ وَاللَّهُ سُبْحَانَهُ وَتَعَالَى أَعْلَمُ .