Musnad Abu Ya'la al-Mawsili 248:31

Narrated to us Ishaq, narrated to us Jarir, from al-A'mash, from al-Musayyib ibn Rafi', from Tamim al-Ta'i, from Jabir ibn Samurah, who said: The Messenger of Allah (peace be upon him) entered the mosque and saw people raising their hands. He said: "What is the matter with them, raising their hands as if they were the tails of stubborn horses? Be still in the prayer."