Praise be to Allah,
Muhammad ibn Fudayl narrated to us from al-Mukhtaar ibn Fulful from Anas ibn Maalik who said, “One day, Allah’s Messenger (PBUH) led us in prayer, and after he had completed the prayer he turned his face towards us and said, ‘0 people, I am your imaam, so do not precede me in bowing, prostrating, standing, sitting or concluding the prayer, for I can see you in front of me and behind me. By the One in whose Hand my soul is, if you had seen what I saw, you would have laughed a little and wept a great deal’ [His companions] asked, ‘Messenger of Allah, what did you see? He replied, ‘I saw Paradise and Hell.”‘
(Musnad Ahmad, Vol. 3, p. 102. The isnaad of this hadeeth is Saheeh according to the conditions set by Muslim.)
Source:
Thulaathiyyaat Musnad Ahmad ibn Hanbal (may Allah have mercy on him)
Reports of Imaam Ahmad that have only three narrators between him and the Prophet, peace, and blessings be upon him.
Shaykh Muhammad ibn Ahmad ibn Saalim as–Saffaareenee al–Hanbalee ~(1114 –1188 AH)