It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that one day the Messenger of Allah (peace and blessings be upon him) led us in prayer. When he completed the prayer, he turned towards us and said: "O people, I am your imam, so do not precede me in bowing and prostration, in standing and in the salam, for I see you in front of me and from behind me." Then he said: "By the One in whose Hand is the soul of Muhammad (peace and blessings be upon him), if you were to see what I have seen, you would laugh little and weep much." The Companions (may Allah be pleased with them) said: O Messenger of Allah, what have you seen? He (peace and blessings be upon him) said: "I have seen Paradise and Hell."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2592