Sahih Muslim Book 4, Hadith Number 957.

Chapter : The duty of the Imam is to be brief and perfect in prayer.

Thabit reported it on the authority of Anas: I have never said such a light and perfect prayer as I said behind the Messenger of Allah (may peace be upon him). The prayer of the Messenger of Allah (may peace be upon him) was well balanced. And so too was the prayer of Abu Bakr well balanced. When it was the time of ‘Umar b. al-Khattab he prolonged the morning prayer. When the Messenger of Allah (may peace be upon him) said: Allah listened to him who praised Him, he stood erect till we said: He has forgotten. He then prostrated and sat between two prostration till we said: He has forgotten.