Sahih Muslim Book 4, Hadith Number 1876.

Chapter : Jumu’a prayer is to be observed when the sun passes over the meridian.

Jabir b. Samura said that the Messenger of Allah (may peace be upon him) used to deliver the sermon while standing. He would then sit down and then stand up and address in a standing posture; and whoever informed you that he (the Holy Prophet) delivered the sermon while sitting told a lie. By Allah, I prayed with him more than two thousand times.