مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3742
Musnad of Abdullah bin Mas'ood
It was narrated that `Abdullah (رضي الله عنه) said: When the Messenger of Allah (ﷺ) died, the Ansar said: A leader from among us and a leader from among you. 'Umar came to them and said: O Ansar, do you not know that the Messenger of Allah (ﷺ) ordered Abu Bakr to lead the people in prayer? Who among you could feel at ease putting himself ahead of Abu Bakr? They said: We seek refuge with Allah from putting ourselves ahead of Abu Bakr.
Musnad Ahmad 3765Its isnad is hasan]