Musannaf Ibn Abi Shayba 3:6070

Abu Mu'awiyah narrated to us, from al-A'mash, from al-Musayyab ibn Rafi', from Tamim ibn Tarafah, from Jabir ibn Samurah, who said: The Messenger of Allah (may Allah bless him and grant him peace) came out to us and said: "What is the matter with me seeing you raising your hands as if they were the tails of restive horses? Be still in the prayer."