It was narrated that Ibn Abbas said:
"I would like the people to reduce (the will) from one third to one quarter, because the Messenger of Allah (ﷺ) said: 'One third is a lot.'" (TR)
English reference (TR): Vol. 3, Book 22, Hadith 2711 (TR)
Arabic reference (TR): Book 22, Hadith 2815 (TR)