«كان يردف خلفه ويضع طعامه على الأرض ويجيب دعوة المملوك ويركب الحمار»
It was the practice of the Prophet (peace and blessings be upon him):
"He (peace and blessings be upon him) would let someone ride behind him, place his food on the ground, accept the invitation of a slave, and ride a donkey."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4945