The best charity
Abu Hurayrah (radi Allahu anhu) said: There came a man to the Prophet (sal Allahu alaihi wa sallam) and said, “O Messenger of Allah, which charity is the most rewardable?” He (sal Allahu alaihi wa sallam) said, “That you should give charity (in a state when you are) healthy and stingy and fear poverty, hoping to become rich (charity in such a state of health and mind is the best). And you must not defer (charity to such a length) that you are about to die and would be saying: ‘This is for so-and-so, and this for so-and-so.’ Lo! It has already come into (the possession of) so-and-so”
[Sahih al-Bukhari and Muslim]
Charity in the real sense is that which a person gives when he is healthy. If a person gives charity when he is facing death, it does not have much value before Allah. Moreover, in that condition he cannot give more than one-third of his property in charity because then it becomes the property of his successors, which cannot be spent even in the way of Allah. For this reason Allah has prescribed a limit in this respect, according to which if a person going through a mortal disease wants to give his property in charity or donate it for some charitable purpose, he cannot spend more than one-third of it on this account. This injunction is an inducement for people to hurry in doing good deeds, especially in the matter of alms and charity. In fact, he should do it without delay.
And Allah Knows Best!