صحيح مسلم

Uqba b. 'Amir reported that Allah's Messenger (ﷺ) one day went out and he offered prayer over the martyrs of Uhud just as prayer is offered over the dead. He then came back and sat on pulpit and said: I shall be present there (at the Cistern) before you. I shall be your witness and, by Allah, I perceive as if I am seeing with my own eyes my Cistern at this very state and I have been given the keys of the treasures of the earth or the keys of the earth and, by Allah, I am not afraid concerning you that you would associate anything (with Allah after me), but I am afraid that you would be vying with one another (for the possession of) the treasures of the earth.