(3) باب الْوَصِيَّةِ بِالثُّلُثِ
It was narrated that Ibn 'Abbas said:
"If the people were to reduce (their bequests) to one-quarter (of their wealth, that would be better), because the Messenger of Allah said: 'One-third, and one-third is much or large.'"
Reference: Sunan an-Nasa'i 3634
In-book reference: Book 30, Hadith 24
English translation: Vol. 4, Book 30, Hadith 3664