The Messenger of Allah ﷺ led us in prayer one day, then turned his face toward us and said, "I am your imam, so do not get ahead of me in bowing, prostrating, standing, or leaving the prayer, for I see you from in front of me and from behind me."Then he said, "By the One in whose hand my soul rests, if you saw what I have seen, you would laugh little and weep much."We asked, "What did you see, Messenger of Allah?"He replied, "I saw Paradise and the Fire."
أخبرنا علي بن حجر قال حدثنا علي بن مسهر عن المختار ابن فلفل
صلى بنا رسول الله ﷺ ذات يوم ثم أقبل علينا بوجهه فقال إني إمامكم فلا تبادروني بالركوع ولا بالسجود ولا بالقيام ولا بالانصراف فإني أراكم من أمامي ومن خلفي ثم قال والذي نفسي بيده لو رأيتم ما رأيت لضحكتم قليلا ولبكيتم كثيرا قلنا ما رأيت يا رسول الله قال رأيت الجنة والنار
Muslim reported it in the Book of Prayer, chapter on the prohibition of preceding the imam in bowing or prostration or the like, hadith no. 426, from Ali bin Hajar with the same chain, and it is also found in Kubra, hadith no. 1286.