Authentic
Sunan Abu Dawud 1956
I saw the Messenger of Allah (ﷺ) addressing the people at Mina (on the day of sacrifice) when the sun rose high (i.e. in the forenoon) on a white mule, and Ali (Allah be pleased with him) was interpreting on his behalf; some people were standing and some sitting.
يَخْطُبُ النَّاسَ بِمِنًى حِينَ ارْتَفَعَ الضُّحَى عَلَى بَغْلَةٍ شَهْبَاءَ وَعَلِيٌّ - رضى الله عنه - يُعَبِّرُ عَنْهُ وَالنَّاسُ بَيْنَ قَاعِدٍ وَقَائِمٍ .