A man came to the Prophet ﷺ and said, "My son's son has died. What is my share of his inheritance?"The Prophet ﷺ replied, "You receive a sixth."When the man turned to leave, he called him back and said, "You receive another sixth."When the man turned to leave again, he called him back and said, "The second sixth is a provision for you."Qatada said, "They do not know alongside whom he inherited it." Qatada also said, "The least the grandfather inherits is a sixth."
حدثنا محمد بن كثير أخبرنا همام عن قتادة عن الحسن
أن رجلا أتى النبي ﷺ فقال إن ابن ابني مات فما لي من ميراثه فقال لك السدس فلما أدبر دعاه فقال لك سدس آخر فلما أدبر دعاه فقال إن السدس الآخر طعمة قال قتادة فلا يدرون مع أي شيء ورثه قال قتادة أقل شيء ورث الجد السدس
[Its isnad is daif] Tirmidhi narrated it, Inheritance, chapter on what has been said regarding the grandfather's inheritance, no. 2099, from the hadith of Hammam through this route, and he said, hasan sahih, and Ibn Jarud graded it sahih, no. 961. Qatada and Hasan narrated with "an" (indicating a possible break in transmission), and the hadith has other daif routes. See Musnad Humaydi, in my edition, nos. 835, 836.