Does a grandmother inherit alongside her son (the deceased's father) if he is alive and an heir?
Chapter on the Roots of Inheritance Shares that Increase (Awl)
Al-Mughni
Book of Inheritance Shares (Farā'id)
Primary text
The grandmother inherits alongside her son. This is the position of 'Umar, Ibn Mas'ud, Abu Musa, 'Imran bin Al-Husayn, Abu Al-Tufayl, Shurayh, Al-Hasan, Ibn Sirin, Jabir bin Zayd, Al-'Anbari, Ishaq, Ibn Al-Mundhir, and it is the apparent view of the madhhab of Ahmad bin Hanbal. The evidence is the narration of Ibn Mas'ud that the first grandmother whom the Messenger of Allah (peace be upon him) granted one-sixth share was the paternal grandmother (mother of the father) while her son was alive. Furthermore, grandmothers are considered mothers and inherit the mother's portion, not the father's portion, thus they are not veiled by the father as mothers of the mother are not veiled by the mother.
Supporting text
Zayd bin Thabit held that the grandmother does not inherit alongside her son, a view narrated from 'Uthman and 'Ali, and held by Malik, Al-Thawri, Al-Awza'i, Sa'id bin 'Abd Al-Aziz, Al-Shafi'i, Ibn Jabir, Abu Thawr, and the companions of opinion (Ahl Al-Ra'y). This view is also narrated from Ahmad by a group of his companions. Their evidence is that she relates through her son, thus she should not inherit with him, analogous to the grandfather with the father, and the maternal grandmother with the mother.