Musnad Ahmad 30:779

Yazid ibn Harun narrated to us, Hisham informed us, from Muhammad, from Abu Hurayrah, who said: "He forbade *al-ikhtisar* (placing the hand on the waist) during prayer." We said to Hisham: "What is *al-ikhtisar*?" He said: "That one places his hand on his waist while he is praying." Yazid said: We said to Hisham: "Did he attribute it to the Prophet, may Allah bless him and grant him peace?" He nodded his head, meaning: "Yes."