Musannaf Ibn Abi Shayba 36:426

Yazid ibn Harun narrated to us, he said: Nafi' ibn 'Umar informed us, from Umayyah ibn Safwan, from Abu Bakr ibn Abi Zuhayr al-Thaqafi, from his father, that he heard the Prophet, may Allah bless him and grant him peace, saying in his sermon at al-Nabatah or al-Nabawah—and al-Nabawah is in al-Ta'if: "You are about to know the people of Paradise from the people of the Fire, and your best from your worst." They said: "By what, O Messenger of Allah?" He said: "By good praise and bad praise. You are the witnesses of Allah upon the earth."