I saw Ibn Umar praying in whatever direction his mount was facing, and he said, "The Messenger of Allah ﷺ used to do this."
حدثنا محمد بن جعفر حدثنا شعبة
رأيت ابن عمر يصلي حيث توجهت به راحلته ويقول كان رسول الله ﷺ يفعله
Its isnad is sahih, and it is a longer version of 5447, see also 5451.