Qays bin Abi Hazim narrates from Sayyiduna Jarir (may Allah be pleased with him) that he said: I could not sit firmly on a horse, so I mentioned that to the Messenger of Allah (peace and blessings be upon him). He (peace and blessings be upon him) struck his hand on my chest, until I saw the mark of his (peace and blessings be upon him) hand on my chest, and said: "O Allah, make him firm and make him one who guides and is rightly guided." After that I never fell from a horse.
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 2241