From Sahih Bukhari (Hadith 493):
Narrated Ibn `Abbas:Once I came riding a she-ass when I had just attained the age of puberty. Allah's Messenger (ﷺ) was offering the prayer at Mina with no wall in front of him and I passed in front of some of the row. There I dismounted and let my she-ass loose to graze and entered the row and nobody objected to me about it
Reference: Bukhari 493