I was riding behind the Prophet ﷺ on a donkey called Ufayr.
كنت ردف النبي ﷺ على حمار يقال له: عفير.
Bukhari narrated it in the Book of Jihad and Expeditions (2856), and Muslim in the Book of Faith (30:49), both through Abu Ahwas Salam bin Salim, from Abu Ishaq, from Amr bin Maymun, from Muaz bin Jabal, who related it.