Sahih Bukhari Volume 4, Book 54, Hadith Number 439.

Narated By Abu Huraira : I heard the Prophet saying, “Who ever spends a couple (of objects) in Allah’s cause, will be called by the Gatekeepers of Paradise who will say, “O so-and-so, come on!” Abu Bakr said, “Such a person will never perish or be miserable’ The Prophet said, “I hope you will be among such person.”