It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that Sayyiduna Umar (may Allah be pleased with him) was asked about the bequest, and Sayyiduna Umar (may Allah be pleased with him) said: A third is right; it is neither too little nor too much.
(6) Chapter: One who held it recommended to bequeath less than a third when he does not leave his heirs well-off, taking as evidence what we have narrated in the hadith of Sa'd bin Abi Waqqas
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الوصايا / 12572