Musnad Ahmad 32:699

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Thabit al-Bunani, from Anas ibn Malik, who said: "The prayer would be called, and the Prophet, peace and blessings of Allah be upon him, would speak to a man regarding a need he had. He would stand between him and the Qiblah, and he would continue standing, speaking to him. I would sometimes see some of the people nodding off due to the length of the Prophet's, peace and blessings of Allah be upon him, standing for him."