It is narrated from Hasan (may Allah have mercy on him) regarding the son of the mal'ana: Whoever leaves behind his mother and the 'asaba (male agnates) of his mother, they said: The mother gets one-third, and whatever remains is for the 'asaba of the mother.
Hadith Referenceسنن دارمي / من كتاب الفرائض / 2993
Hadith Gradingتحقیق (حسین سلیم أسد الدارانی):إسناده صحيح إلى الحسن، [مكتبه الشامله نمبر: 3003]
Hadith Takhrijاس اثر کی سند حسن رحمہ اللہ تک صحیح ہے۔ دیکھئے: [ابن أبى شيبه 11383] ، [البيهقي 258/6]