Musnad Ahmad 31:390

Surayj ibn al-Nu‘man narrated to us, Hammad narrated to us, from al-Hajjaj, from ‘Atiyyah ibn Sa‘d, from Abu Sa‘id al-Khudri, who said: The people of the camels boasted in the presence of the Messenger of Allah, peace and blessings of Allah be upon him. The Messenger of Allah, peace and blessings of Allah be upon him, said: "Tranquility and dignity are in the people of the sheep, and boasting and arrogance are in the people of the camels."