Sahih Bukhari, Chapter: Obligatory Charity Tax (Zakat)

I heard the Prophet saying, "O people! Give in charity as a time will come upon you when a person will wander about with his object of charity and will not find anybody to accept it, and one (who will be requested to take it) will say, "If you had brought it yesterday, would have taken it, but to-day I am not in need of it."