Sahih Bukhari Volume 007, Book 064, Hadith Number 266.

Narrated By Sad : The Prophet visited me at Mecca while I was ill. I said (to him), "I have property; May I bequeath all my property in Allah's Cause?" He said, "No." I said, "Half of it?" He said, "No." I said, "One third of it?" He said, "One-third (is alright), yet it is still too much, for you'd better leave your inheritors wealthy than leave them poor, begging of others. Whatever you spend will be considered a Sadaqa for you, even the mouthful of food you put in the mouth of your wife. Anyhow Allah may let you recover, so that some people may benefit by you and others be harmed by you."