Tamim bin Tarafah narrates from Sayyiduna Jabir (may Allah be pleased with him): The Prophet (peace and blessings be upon him) came out and entered the mosque, and saw the people raising their hands, and he said: "Why is it that I see the people raising their hands like the tails of unruly horses? Be still in prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 1814