From Sahih Muslim (Hadith 1599):
Wahb al-Khuza'i reported:I prayed behind the Messenger of Allah (ﷺ) at Mina, and there was the greatest number of people, and they prayed two rak'ahs on the occasion of the Farewell Pilgrimage. (Muslim said: Haritha b. Wahb al-Khuza'i is the brother of 'Ubaidullah b. 'Umar son of Khattab from the side of his mother)
Reference: Muslim 1599