Authentic
graded by Al-Albani
Mishkat al-Masabih 4363
وَعَن هلالِ بن عَامر عَن أَبِيه قَالَ: رَأَيْتُ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ بِمِنًى يَخْطُبُ عَلَى بَغْلَةٍ وَعَلَيْهِ بُرْدٌ أَحْمَرُ وَعَلِيٌّ أَمَامَهُ يُعَبِّرُ عَنْهُ. رَوَاهُ أَبُو دَاوُدَ
Hilal b. ‘Amir quoted his father as saying he saw the Prophet in Mina on a she-mule giving an address, wearing a red cloak, with ‘Ali in front of him repeating what he said. (This was because the crowd was too large for all to hear the Prophet. ‘AIi was repeating his words for the benefit of those too far away to bear the address) Abu Dawud transmitted it.
Cited in Mishkat al-Masabih (No. 4363).