Sayyiduna Mas'ud (may Allah be pleased with him), who was the slave of Farwah Abu Tamim, the grandfather (of Buraydah bin Sufyan), said: The Messenger of Allah (peace and blessings be upon him) and Sayyiduna Abu Bakr (may Allah be pleased with him) passed by me, and Sayyiduna Abu Bakr (may Allah be pleased with him) said to me: O Mas'ud! Go to your master Abu Tamim and tell him to send with us a guide who will take us by the most hidden route, along with a camel and provisions. So I came to my master and told him this, and he sent me and sent with me a camel and a skin of milk. I came to the two of them, and the Messenger of Allah (peace and blessings be upon him) stood up for prayer, with Sayyiduna Abu Bakr (may Allah be pleased with him) on his right - I stood behind the Messenger of Allah (peace and blessings be upon him) and Abu Bakr, and the Messenger of Allah (peace and blessings be upon him) placed his hand on Sayyiduna Abu Bakr's chest and moved him back, so the two of us stood behind him.
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17915