Musnad Ahmad 30:2059

Mu'awiyah narrated to us, he said: Za'idah narrated to us, from Hisham ibn Hassan, from Muhammad ibn Sirin, from Abu Hurairah, he said: "The Messenger of Allah, peace and blessings of Allah be upon him, forbade that a man should pray while 'mukhtasiran' (placing his hands on his hips)."