Sahih Muslim Book 5, Hadith Number 2227.

Chapter : Proof of reward for the giver of charity even if it goes into the hands of and undeserving person.

Abu Haraira reported that the likeness of one who spends or one who gives charity is that of a person who has two cloaks or two coats-of-mail over him right from the breast to the collar bones. And when the spender (and the other narrator said, when the giver of charity) makes up his mind to give charity, it (coat-mail) becomes expanded for him. But when a miserly person intends to spend, it contracts and every ring grips the place where it is. For the giver of charity, this coat-of-mail expands to cover his whole body and obliterates even his footprints. Abu Huraira said: (The miserly man) tries to expand it (the coat-of-mail) but it does not expand.