Yahya related to me from Malik from Hisham ibn Urwa from hisfather that the Messenger of Allah, may Allah bless him and grant himpeace, prayed four raka prayers with only two rakas when at Mina, andthat Abu Bakr prayed them at Mina with only two rakas, and that Umaribn al-Khattab prayed them at Mina with only two rakas, and thatUthman prayed them at Mina with only two rakas for half of hiskhalifate, and then later completed them.
USC-MSA web (English) reference: Book 20, Hadith 210
Arabic reference: Book 20, Hadith 908