Musnad Abu Ya'la al-Mawsili 131:17

Abu Khaythama narrated to us, Muhammad ibn Fudayl narrated to us, al-Mukhtar ibn Fulful narrated to us, from Anas ibn Malik, who said: The Messenger of Allah (may Allah bless him and grant him peace) turned away from the prayer one day and faced us. He said: "O people, I am your Imam, so do not precede me in bowing, nor in prostration, nor in standing, nor in sitting, nor in departing. For indeed, I see you from in front of me and from behind me." "And by the One in Whose hand is my soul, if you saw what I saw, you would laugh little and weep much." They said: "O Messenger of Allah, what did you see?" He said: "I saw Paradise and the Fire."