Musnad Ahmad 937:66

Waki’ narrated to us, Sufyan narrated to us, from Habib, from Maymun ibn Abi Shabib, from Abu Dharr, that the Prophet, peace and blessings of Allah be upon him, said to him: "Fear Allah wherever you are, and follow up a bad deed with a good deed, it will erase it, and treat people with good character." Waki’ said: And Sufyan said once: From Mu’adh, "And I found in my book: From Abu Dharr, and it is the first hearing."