Musnad Ahmad 30:2948

'Abd al-Rahman narrated to us, he said: Sulaym narrated to us, from his father, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Beware of suspicion, for suspicion is the most untruthful of speech. Do not spy, do not pry, do not hate one another, do not envy one another, do not compete against one another, and do not turn your backs on one another. And be, O servants of Allah, brothers."