Musnad Abu Ya'la al-Mawsili 42:230

Zuhayr narrated to us, Abu Mu'awiyah narrated to us, al-A'mash narrated to us, from Isma'il ibn Raja', from his father, and from Qays ibn Muslim, from Tariq ibn Shihab, both of them from Abu Sa'id, who said: I heard the Messenger of Allah (may Allah bless him and grant him peace) saying: "Whoever among you sees an evil, and he is able to change it with his hand, then let him do so. If he is not able to do so with his hand, then with his tongue. If he is not able to do so with his tongue, then with his heart, and that is the weakest of faith."