Muwatta Malik, Book 20, Hadith 210 (USC-MSA) ⓘ

Yahya related to me from Malik from Hisham ibn Urwa from his father that the Messenger of Allah, may Allah bless him and grant him peace, prayed four raka prayers with only two rakas when at Mina, and that Abu Bakr prayed them at Mina with only two rakas, and that Umar ibn al-Khattab prayed them at Mina with only two rakas, and that Uthman prayed them at Mina with only two rakas for half of his khalifate, and then later completed them.

وَحَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم صَلَّى الصَّلاَةَ الرُّبَاعِيَّةَ بِمِنًى رَكْعَتَيْنِ وَأَنَّ أَبَا بَكْرٍ صَلاَّهَا بِمِنًى رَكْعَتَيْنِ وَأَنَّ عُمَرَ بْنَ الْخَطَّابِ صَلاَّهَا بِمِنًى رَكْعَتَيْنِ وَأَنَّ عُثْمَانَ صَلاَّهَا بِمِنًى رَكْعَتَيْنِ شَطْرَ إِمَارَتِهِ ثُمَّ أَتَمَّهَا بَعْدُ ‏.‏