Musnad Ahmad 482:53

Hajjaj ibn Muhammad narrated to us, Layth ibn Sa’d narrated to us, Yazid ibn Abi Habib narrated to me, from Abu al-Khayr, from Uqbah ibn Amir: That the Messenger of Allah (peace and blessings of Allah be upon him) went out one day and prayed over the people of Uhud as he prayed over the dead. Then he turned to the pulpit and said: "I am a forerunner for you, and I am a witness over you. And I, by Allah, am looking at my Basin right now. Behold, I have been given the keys to the treasures of the earth—or the keys of the earth. And I, by Allah, do not fear that you will commit shirk after me, but I fear for you that you will compete with one another for it."