It is narrated from Uqbah bin Amir (may Allah be pleased with him) that one day he (peace and blessings be upon him) went out and offered prayer over the martyrs of Uhud just as the funeral prayer is offered, then he (peace and blessings be upon him) turned to the minbar and said: "I am your forerunner and I am a witness over you. By Allah, I am now looking at the Pond (al-Kawthar), and indeed I have been given the keys of the treasures of the earth (or he (peace and blessings be upon him) said: the keys of the earth). And he said: By Allah, I do not fear that you will commit shirk after me; rather, I fear that you will become entangled in the world."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6809