Musannaf Ibn Abi Shayba 13:1787

Abu Bakr narrated to us, he said: Ibn Abi Za’idah narrated to us, from Ibn ‘Awn, from Muhammad, who said: Shurayh said: "Claim, increase, and be eloquent, and bring just witnesses for that, for we have been commanded to [accept] the just. And come, and ask about him; if they say, 'Allah knows best,' then Allah knows best. If they differentiate by saying, 'He is suspicious,' then the testimony of a suspicious person is not permissible. But if they say, 'We have known him only as a just Muslim,' then he is, if Allah wills, likewise, and his testimony is permissible."