Sunan An-Nasai, Chapter: The Book of Leading the Prayer (Al-Imamah)

that a slave of his grandfather who was called Masud said: "The Messenger of Allah (saw) and Abu Bakr passed by me and Abu Bakr said to me: 'O Masud, go to Abu Tamim - meaning the man from whom he had been freed - 'and tell him to give us a camel so that we could ride, and let him send us some food and a guide to show us the way.' So I went to my former master and told him the same, and he sent with me a camel and vessels of milk, and I brought them via a secret route. Then the time for prayer came and the Messenger of Allah (saw) stood up and prayed, and Abu Bakr stood to his right. I had come to know about Islam and I was with them, so I came and stood behind them. So the Messenger of Allah (saw) pushed Abu Bakr on the chest (to make him move backward) and we stood behind him." Abu Abdur-Rahman (An-Nasai) said: (This) Buraidah is not a reliable narrator of Hadith. (Daif)