Sahih Al Bukhari (601)

عن ابن عمر رضي الله عنهما {أنه كان مع النبي (صلى الله عليه وسلم) في سفر فكان على بكر لعمر صعب فكان يتقدم النبي (صلى الله عليه وسلم) فيقول أبوه يا عبد الله لا يتقدم النبي (صلى الله عليه وسلم) أحد فقال له النبي (صلى الله عليه وسلم) بعنيه فقال عمر هو لك فاشتراه ثم قال هو لك يا عبد الله فاصنع به ما شئت}.

Narrated Ibn `Umar: That he was in the company of the Prophet (peace be upon him) on a journey, riding a troublesome camel belonging to `Umar. The camel used to go ahead of the Prophet (peace be upon him), so Ibn `Umar's father would say: "O `Abdullah! No one should go ahead of the Prophet (peace be upon him)." The Prophet (peace be upon him) said to him: "Sell it to me." `Umar said to the Prophet (peace be upon him) "It is for you." So, he bought it and said: "O `Abdullah! It is for you, and you can do with it what you like."