I saw the Prophet ﷺ praying on the day of the Conquest, and he placed his sandals on his left side.
حدثنا مسدد حدثنا يحيى عن ابن جريج حدثني محمد بن عباد بن جعفر عن ابن سفيان
رأيت النبي ﷺ يصلي يوم الفتح ووضع نعليه عن يساره
Its isnad is sahih. Nasai narrated it in the Book of Qibla, chapter on where the imam should place his sandals when leading the people in prayer, hadith no. 777, and Ibn Majah, hadith no. 1431, from the hadith of Yahya Qattan through this route.