Sahih Muslim Book 4, Hadith Number 1021.

Chapter : The excellence of the prayer and the way it is begun and the excellence of Ruku’ and moderation in it and prostration and moderation in it, etc.

This Hadith has been narrated by Ibn ‘Uyaina on the authority of al-Zuhri with the same chain of transmitters and he reported: The Apostle of Allah (may peace be upon him) was leading prayer at ‘Arafa.