Sahih al-Bukhari 2743
صحيح البخاري#2743SahihNarrated 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 Messenger (ﷺ) said, "One-third, yet even one third is too much
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 55:6