Sahih Bukhari Volume 7, Book 72, Hadith Number 849.

Narrated By Aiyub : The worst of three (persons riding one, animal) was mentioned in ‘Ikrima’s presence ‘Ikrima said, “Ibn ‘Abbas said, ‘(In the year of the conquest of Mecca) the Prophet came and mounted Qutham in front of him and Al-Fadl behind him, or Qutham behind him and Al-Fadl in front of him.’ Now which of them was the worst off and which was the best?”