Tamim bin Tarafah narrates from Sayyiduna Jabir bin Samurah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) came out to them (I think the narrator said: in the mosque) while they were raising their hands, and he said: "Why is it that I see you raising your hands like the tails of unruly horses? Be still in prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 1813