Musnad Ahmad 30:1235

Abu al-Nadr narrated to us, al-Mubarak ibn Fudalah narrated to us, from al-Hasan, from Abu Hurayrah, who said—I do not know it except from the Prophet, may Allah bless him and grant him peace—he said: "Upon every joint of the son of Adam is a charity every morning." This became difficult for the Muslims, so the Messenger of Allah, may Allah bless him and grant him peace, said: "Your greeting to the servants of Allah is a charity, your removing of harm from the road is a charity, your enjoining of good is a charity, and your forbidding of evil is a charity." And he mentioned things similar to this which I did not memorize.