Musnad Ahmad 907:5

Yazid narrated to us, Mas'ar informed us, from Ubayd Allah ibn al-Qibtiyya, from Jabir ibn Samura, who said: When we prayed behind the Messenger of Allah (peace and blessings of Allah be upon him), we would say "As-salamu alaykum" while gesturing with our hands to the right and to the left. The Messenger of Allah (peace and blessings of Allah be upon him) said: "What is the matter with people who wave their hands as if they were the tails of restive horses? Should not one of you remain still, gesture with his hand upon his thigh, then greet his companion to his right and to his left?"