Sahih Muslim
The Book of Zakat (Kitab Al-Zakat)
Book Number: 005 / Hadith Number: 2251
Abu Huraira reported that a person came to the Apostle of Allah (may peace be upon him) and said: Messenger of Allah, which charity is the greatest in reward? (The Holy Prophet said): By your father, beware, you should give charity (in a state when you are) healthy and close-fisted, haunted by the fear of poverty, and still hoping to live (as rich). And you must not defer charity (to the time) when you are about to die, and would then say:" This is for so and so, and this for so and so." It has already become the possession of so and so.