Sunan Ibn Majah, Volume 3, Book 22, Hadith 2711 (DarusSalam) ⓘ
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 said: 'One third is a lot.'”
حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا وَكِيعٌ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنِ ابْنِ عَبَّاسٍ، قَالَ وَدِدْتُ أَنَّ النَّاسَ، غَضُّوا مِنَ الثُّلُثِ إِلَى الرُّبُعِ لأَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " الثُّلُثُ كَبِيرٌ - أَوْ كَثِيرٌ - " .
also referenced under: Hadith 2711 (Reference) & Book 22, Hadith 2815 (In-Book)