Musnad Ahmad

Mus'ab bin Thabit, may Allah have mercy on him, says that there was a wooden post at the place where the Imam stands in the Prophet's Mosque. We tried very hard to find out something about it from someone, but we could not find a single person who could tell us anything about it. Coincidentally, Muhammad bin Muslim, the owner of the Maqsura, told me that one day Hazrat Anas, may Allah be pleased with him, was sitting with me. He said, "Do you know why this wooden post was placed here?" I had not asked him this question. I replied, "By Allah! I do not know why it was placed here." He said, "The Prophet, peace and blessings be upon him, used to place his right hand on it and turn towards us and say, 'Straighten up and align your rows.'"