Musnad Ahmad 30:3386

Yazid narrated to us, Muhammad ibn ‘Amr informed us, from Abu Salamah, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I have been aided by fear, I have been given the concise speech, and the earth has been made for me a place of prayer and a means of purification. And while I was sleeping, I was brought the keys to the treasures of the earth, and they were placed in my hand."