Musnad Ahmad 30:3244

Bahz narrated to us, and 'Affan narrated to us, he said: Sulaym ibn Hayyan narrated to us, he said: I heard my father narrating from Abu Hurayrah, who said: The Messenger of Allah, may Allah bless him and grant him peace, said: "Beware of suspicion, for suspicion is the most untruthful of speech. Do not spy, do not pry, do not envy one another, do not compete against one another, do not hate one another, and do not turn your backs on one another. And be, O servants of Allah, brothers."