(3) باب الْوَصِيَّةِ بِالثُّلُثِ
Narrated 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."
Reference: Sahih al-Bukhari 2743
In-book reference: Book 55, Hadith 6
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 4, Book 51, Hadith 6