Musnad Ahmad 32:294

Yazid ibn Harun narrated to us, Hammad ibn Salamah informed us, from Thabit al-Bunani, from Anas, who said: "When the Messenger of Allah (peace and blessings of Allah be upon him) migrated, the Messenger of Allah (peace and blessings of Allah be upon him) would ride, and Abu Bakr would be his rider behind him. Abu Bakr was known on the road due to his frequent traveling to Ash-Sham. He would pass by people, and they would say: 'Who is this in front of you, O Abu Bakr?' He would say: 'A guide who guides me.' When they drew near to Medina, they sent word to the people who had accepted Islam from the Ansar, to Abu Umamah and his companions. They went out to them and said: 'Enter, safe and obeyed.' So they entered." Anas said: "I have never seen a day more radiant or more beautiful than the day the Messenger of Allah (peace and blessings of Allah be upon him) and Abu Bakr entered Medina. And I witnessed his death, and I have never seen a day more dark or more ugly than the day the Messenger of Allah (peace and blessings of Allah be upon him) died."