Sahih Bukhari Volume 003, Book 050, Hadith Number 879.
Narated By Jabir : While I was riding a (slow) and tired camel, the Prophet passed by and beat it and prayed for Allah's Blessings for it. The camel became so fast as it had never been before. The Prophet then said, "Sell it to me for one Uqiyya (of gold)." I said, "No." He again said, "Sell it to me for one Uqiyya (of gold)." I sold it and stipulated that I should ride it to my house. When we reached (Medina) I took that camel to the Prophet and he gave me its price. I returned home but he sent for me (and when I went to him) he said, "I will not take your camel. Take your camel as a gift for you." (Various narrations are mentioned here with slight variations in expressions relating the condition that Jabir had the right to ride the sold camel up to Medina).