It is narrated from Qatadah (may Allah have mercy on him) that Sayyiduna Ali and Sayyiduna Ibn Mas'ud (may Allah be pleased with them both) said regarding the son of a woman who underwent li'an, who left behind a brother and his mother: For the brother is a third, and for the mother also a third. Sayyiduna Zayd (may Allah be pleased with him) said: For the mother is a third, for the brother a sixth, and the rest goes to the public treasury (bayt al-mal).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الفرائض / 12494