Bukhari Collection: ::Book Number 8:: Hadith # 51
Narrated Abu Musa Al-Ash`ari:The Prophet said, "On every Muslim there is enjoined (a compulsory) Sadaqa (alms)." They (the people) said, "If one has nothing?' He said, "He should work with his hands so that he may benefit himself and give in charity." They said, "If he cannot work or does not work?" He said, "Then he should help the oppressed unhappy person (by word or action or both)." They said, "If he does not do it?" He said, "Then he should enjoin what is good (or said what is reasonable).' They said, "If he does not do that''' He said, "Then he should refrain from doing evil, for that will be considered for Him as a Sadaqa (charity) . "