Musnad Ahmad 30:3121

Surayj ibn al-Nu‘man narrated to us, he said: Fulayh narrated to us, from Hilal ibn ‘Ali, from ‘Abd al-Rahman ibn Abi ‘Amrah, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "Beware of suspicion, for suspicion is the most untruthful of speech. Do not spy, do not compete [in worldly matters], do not turn your backs on one another, and do not hate one another. And be, O servants of Allah, brothers."