Musnad Abu Ya'la al-Mawsili 245:36

Ja'far ibn Muhammad ibn al-Fudayl al-Rasi narrated to us, Muhammad ibn Yusuf al-Firyabi narrated to us, Sufyan narrated to us, from Thawr, from Rashid ibn Sa'd, from Mu'awiyah ibn Abi Sufyan, who said: I heard the Prophet, may Allah bless him and grant him peace, saying: "If you pursue the faults of the people, you will corrupt them, or you will nearly corrupt them." He said: Abu al-Darda' says a word that Mu'awiyah heard from the Messenger of Allah, may Allah bless him and grant him peace, saying: Allah benefited him by it.