أَخْبَرَنَا مُحَمَّدُ بْنُ سَلَمَةَ، قَالَ حَدَّثَنَا ابْنُ وَهْبٍ، عَنْ يُونُسَ، عَنِ ابْنِ شِهَابٍ، قَالَ أَخْبَرَنِي عُبَيْدُ اللَّهِ بْنُ عَبْدِ اللَّهِ بْنِ عُمَرَ، عَنْ أَبِيهِ، قَالَ صَلَّى رَسُولُ اللَّهِ صلى الله عليه وسلم بِمِنًى رَكْعَتَيْنِ وَصَلاَّهَا أَبُو بَكْرٍ رَكْعَتَيْنِ وَصَلاَّهَا عُمَرُ رَكْعَتَيْنِ وَصَلاَّهَا عُثْمَانُ صَدْرًا مِنْ خِلاَفَتِهِ ‏.‏

'Ubaidullah bin 'Abdullah bin Umar narrated that: His father said: "The Messenger of Allah (PBUH) prayed two rak'ahs in Mina, and Abu Bakr prayed two rak'ahs, and Umar prayed two rak'ahs, and Uthman prayed (two rak'ahs) at the beginning of his Khilafah." Translation Not Available

Book reference: Sunan An Nisai Book 15 Hadith 1451
Web reference: Sunan An Nisai Volume 2 Book 15 Hadith 1452