Musnad Ahmad 26:292

Mu'awiyah ibn 'Amr narrated to us, Za'idah narrated to us, 'Asim narrated to us, from Zirr, from 'Abdullah, who said: When the Prophet, peace and blessings of Allah be upon him, was taken [passed away], the Ansar said: "An amir from us, and an amir from you." 'Umar came to them and said: "O assembly of the Ansar, do you not know that the Messenger of Allah, peace and blessings of Allah be upon him, ordered Abu Bakr to lead the people in prayer?" They said: "Yes." He said: "Then which of you finds it agreeable to himself to step forward before Abu Bakr?" The Ansar said: "We seek refuge in Allah from stepping forward before Abu Bakr."