Sahih Bukhari
Sahih Bukhari Volume 004, Book 051, Hadith Number 006.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 51. Wills and Testaments (Wasaayaa)
Narated By Ibn 'Abbas : I recommend that people reduce the proportion of what they bequeath by will to the fourth (of the whole legacy), for Allah's Apostle said, "One-third, yet even one third is too much."