Sahih Bukhari Volume 4, Book 52, Hadith Number 273.

Narated By Jarir : Allah’s Apostle did not screen himself from me since my embracing Islam, and whenever he saw me he would receive me with a smile. Once I told him that I could not sit firm on horses. He stroke me on the chest with his hand and said, “O Allah! Make him firm and make him a guiding and a rightly-guided man.”