مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4008
Musnad of Abdullah bin Mas'ood
It was narrated that 'Abdur-Rahman bin Yazeed said: 'Abdullah said - When he saw 'Uthman pray four rak’ahs in Mina -: I prayed two rak'ahs behind the Messenger of Allah (ﷺ), and two rak'ahs behind Abu Bakr, and two rak'ahs behind ‘Umar. I hope that out of four, two rak'ahs will be accepted from me.
Musnad Ahmad 4034lts isnad is saheeh, al-Bukhari (1657)]