Tamim bin Tarafah narrates from Sayyiduna Jabir (may Allah be pleased with him): The Messenger of Allah (peace and blessings be upon him) came to us in the mosque and saw that they were raising their hands in prayer, and he said: "Why is it that I see them raising their hands like the tails of unruly horses? Be still in prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب الجيم / 1812