Musnad Ahmad 26:46

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Ibrahim, from 'Abd al-Rahman ibn Yazid, who said: 'Uthman prayed four [rak'ahs] in Mina. So 'Abdullah [ibn Mas'ud] said: "I prayed with the Prophet, may Allah bless him and grant him peace, in Mina two rak'ahs, and with Abu Bakr two rak'ahs, and with 'Umar two rak'ahs."