Sahih Bukhari | Volume 8 | Hadith Number 434
Narrated by 'Uqba bin 'Amir
The Prophet went out and offered the funeral prayer for the martyrs of the (battle of) Uhud and then ascended the pulpit and said, "I am your predecessor and I am a witness against you. By Allah, I am now looking at my Tank-lake (Al-Kauthar) and I have been given the keys of the treasures of the earth (or the keys of the earth). By Allah! I am not afraid that after me you will worship others besides Allah, but I am afraid that you will start competing for (the pleasures of) this world."