Ibn 'Abbas (RA) said: (I wish) if people would reduce from third to fourth (part for making a will of their property), for Allah's Messenger (ﷺ) 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".
Hadith Commentary:Benefits and Issues: Statements from some Companions (radi Allahu anhum) and Followers (tabi‘in) have been transmitted regarding making it less than a quarter. The fundamental principle is that the person making the bequest should consider the amount of his estate, the number of his heirs, and their needs, and thus make it less than a third. However, during his lifetime, he may spend as much as he wishes in the way of Allah (fi sabilillah) or on righteous deeds; there is no restriction upon this.
Source: Tuhfat al-Muslim: Commentary on Sahih Muslim, Page: 4218
Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: If people suffice with making a will for one-fourth (of their wealth), then this is more preferable to me, because the Noble Prophet (peace and blessings be upon him) said: "A third (is permitted for making a will), but even a third is much."
Shaykh Muhammad Ibrahim bin Basheer
Benefit: In this hadith, the limit of bequest (wasiyyah) has been specified: it is permissible to make a bequest for up to one third of one’s wealth; making a bequest for more than this is not allowed. Unfortunately, some people, out of anger or excessive love for someone, make a bequest for their entire wealth—this is a sin, and it is not effective. If a person makes such a bequest, it will not be acted upon.
Source: Musnad al-Humaydi: Commentary by Muhammad Ibrahim bin Bashir, Page: 531