. Abu Musa Al-Ash`ari (May Allah be pleased with him) reported: The Prophet (PBUH) said, "Giving in charity is an obligation upon every Muslim". It was said (to him): "What about one who does not find (the means) to do so?'' He (PBUH) said, "Let him work with his hands, thus doing benefit to himself and give in charity.'' It was said to him: "What if he does not have (the means) to do so?'' He (PBUH) said, "Then let him assist the needy, the aggrieved.'' It was said: "What about if he cannot even do this?'' He (PBUH) said, "Then he should enjoin good.'' He was asked: "What if he cannot do that?'' He (the Prophet (PBUH)) said, "He should then abstain from evil, for verily, that is a charity from him".
[Al-Bukhari and Muslim].