Musnad Ahmad 32:1583

Abu Sa’id narrated to us, Za’idah narrated to us, al-Mukhtar ibn Fulful narrated to us, from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "By the One in Whose hand is my soul, if you saw what I saw, you would laugh little and weep much." They said: "And what did you see, O Messenger of Allah?" He said: "I saw Paradise and the Fire." He urged them to pray, and he forbade them from preceding him in bowing and prostration, and he forbade them from departing before he departed from the prayer. And he said: "Indeed, I see you from behind me and from in front of me."