Sahih Bukhari

Narated By Anas : The Prophet had a she camel called Al Adba which could not be excelled in a race. (Humaid, a sub-narrator said, "Or could hardly be excelled.") Once a bedouin came riding a camel below six years of age which surpasses it (i.e. Al'Adba) in the race. The Muslims felt it so much that the Prophet noticed their distress. He then said, "It is Allah's Law that He brings down whatever rises high in the world."