Sahih Muslim Book 4, Hadith Number 1356.

Chapter : Desirability of observing the morning prayer at earlier hour and that is the time when there is darkness before dawn and the exposition about the length of recitation in it.

Abu Dharr reported: The Messenger of Allah (may peace be upon him) struck my thigh and said: How would you act if you survive among the people who would delay prayers beyond their (prescribed) time? He (Abu Dharr) said: What do you command (under this situation)? He (the Holy Prophet) slid: Observe prayer at its prescribed time, then go (to meet) your needs, and if the Iqama is pronounced, and you are present in the mosque, then observe prayer (along with the Jama’at).