I saw the Messenger of Allah ﷺ addressing the people on the Day of Arafah, mounted on a camel, standing in the stirrups.
حدثنا وكيع حدثني عبد المجيد أبو عمرو حدثني
رأيت رسول الله ﷺ يخطب الناس يوم عرفة على بعير قائما في الركابين
Its isnad is sahih. Abdul-Majid Abu Amr is Ibn Wahb, also known as Abdul-Majid bin Abu Yazid. He is trustworthy, and his hadith is found among the Four. Abu Dawud narrated the hadith, 2/196, no. 1917, in the Rites chapter, on delivering the sermon from the pulpit. This hadith has already been narrated by a number of the companions. See 18629.