Sahih Bukhari | Volume 5 | Hadith Number 411

Narrated by Uqba
One day the Prophet went out and offered the (funeral) prayer for the people (i.e. martyrs) of Uhud as he used to offer a funeral prayer for any dead person, and then (after returning) he ascended the pulpit and said, "I am your predecessor before you, and I am a witness upon you, and I am looking at my Tank just now, and I have been given the keys of the treasures of the world (or the keys of the world). By Allah, I am not afraid that you will worship others besides Allah after me, but I am afraid that you will compete with each other for (the pleasures of) this world."