Sahih Al Bukhari – Book of Wills And Testaments (Wasaayaa)

Volumn 004, Book 051, Hadith Number 011. 
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Narated By Abu Huraira RA : A man asked the Prophet, "O Allah's Apostle PBUH ! What kind of charity is the best?" He replied. "To give in charity when you are healthy and greedy hoping to be wealthy and afraid of becoming poor. Don't delay giving in charity till the time when you are on the death bed when you say, 'Give so much to so-and-so and so much to so-and so, and at that time the property is not yours but it belongs to so-and-so (i.e. your inheritors)."