Sahih Muslim Book 13, Hadith Number 4000.

Chapter : Will can be made only for one-third.

Ibn ‘Abbas (Allah be pleased with them) said: (I wish) if people would reduce from third to fourth (part for making a will of their property), for Allah’s Messenger (may peace be upon him) said: So far as the third (part) is concerned it is quite substantial. In the hadith transmitted on the authority of Waki (the words are) “large” or “much”.