Abu Dawud Book 3, Hadith Number 1631.

Narated By Ata ibn Yasar : The Prophet (PBUH) said: Sadaqah may not be given to rich man, with the exception of five classes: One who fights in Allah’s path, or who collects it, or a debtor, or a man who buys it with his money, or a man who has a poor neighbour who has been given sadaqah and gives a present to the rich man.