Musnad Abu Ya'la al-Mawsili 110:107

Muhammad ibn Bakkar narrated to us, al-Walid ibn Abi Thawr narrated to us, from Simak, from Ikrimah, from Ibn Abbas, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Upon every joint of a human being is a charity (sadaqah)." A man from the people said, "This is difficult, and who can bear this?" He said, "Enjoining the good and forbidding the evil is a charity. Helping the weak is a charity. And every step one of you takes toward prayer is a charity."