Abu Dawud Book 11, Hadith Number 2859.
Chapter : Disapproval of causing injury to anyone by a will.
Narated By Abu Hurairah : A man asked the Apostle of Allah (PBUH): Apostle of Allah, which sadaqah (charity) is the best? He replied: (The best sadaqah is) that you give something as sadaqah (charity) when you are healthy, greedy, expect survival and fear poverty, and not that you postpone it until your death, and then you say: For so-and-so is such-and-such, and for so-and-so is such-and-such, while it was already for so-and-so.