Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1486
Wahb al-Khuza'i reported: I prayed behind the Messenger of Allah (way peace be upon him) at Mina, and there was the greatest number of people, and they prayed two rak'ahs on the occasion of the Farwell Pilgrmage. (Muslim said: Haritha b. Wahb al-Khuza'i is the brother of 'Ubaidullah b. 'Umar son of Khattab from the side of mother.)