Musnad Ahmad 32:1627

'Affan narrated to us, 'Abd al-Wahid narrated to us, al-Mukhtar ibn Fulful narrated to us, Anas ibn Malik narrated, saying: The Messenger of Allah (peace and blessings of Allah be upon him) performed a prayer, then he turned his face toward us and said: "I am your Imam, so do not precede me in bowing, nor in prostration, nor in standing, for I see you from in front of me and from behind me." Then he 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: "O Messenger of Allah, and what did you see?" He said: "I saw Paradise and the Fire."