Musnad Ahmad 30:2871

Ishaq narrated to us, Malik narrated to me, from Abu al-Zinad, from al-A’raj, from Abu Hurairah, that 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 compete (in worldly matters), do not envy one another, do not hate one another, and do not turn your backs on one another. And be, O servants of Allah, brothers."