Giving one's entire wealth in charity - a Sharee‘ah viewpoint
1-4-2013 | IslamWeb
Question:
Is there a minimum limit for paying charity and participating in charitable projects? Also, is there a maximum limit for charitable deeds such as donating money? I posed this question because some people say that charity has a minimum and a maximum (for example Zakaah is the minimum and the third of one's wealth is the maximum according to the claim of some people). Kind regards.
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
One may totally dispose of his money by donating it or giving it in charity or whatever and there is no maximum limit for this. Rather, it is permissible for one to give all his wealth in charity. However, he should not do so unless he enjoys a high level of satisfaction, patience and contentment. Ka‘b ibn Maalik 
wanted to give all his wealth in charity but the Prophet, sallallaahu ‘alayhi wa sallam, instructed him to keep a portion of it. An-Nawawi 
after mentioning the Hadeeth about the repentance Allaah The Almighty Accepted from Ka‘b ibn Maalik said in Sharh Saheeh Muslim: "The Prophet, sallallaahu ‘alayhi wa sallam, ordered him to confine himself to giving a portion thereof in charity out of his fear for him of being harmed by poverty and out of fear that he would not have patience to bear a hard life. This does not contradict that Abu Bakr gave all his wealth in charity as he was patient and satisfied."
Giving all one's wealth in charity is approved according to some scholars. This was stated in Al-Muntaqa by Al-Baaji who is a Maaliki scholar. Ibn Naafi‘ said in An-Nawaadir: "It avails him to give a third."
What was said about the minimum limit for charity is correct which is paying the obligatory Zakah. Concerning the maximum, in the life of the giver of charity, it is as we mentioned. Concerning the charity suspended on death, which is called a will, Allaah The Almighty Allowed writing a will regarding the third of one's wealth or less. What exceeds this amount in a will may not be executed unless the inheritors approve.
Allaah Knows best.