To whom is the surplus of the inheritance returned when fixed-share heirs do not exhaust the estate, excluding the spouse?
Chapter on the Roots of Inheritance Shares that Increase (Awl)
Al-Mughni
Book of Inheritance Shares (Farā'id)
Primary text
When the deceased leaves only fixed-share heirs who do not exhaust the entire estate, such as daughters, sisters, and grandmothers, the remaining surplus is returned to them proportionally according to their fixed shares. This view is narrated from Umar, Ali, Ibn Mas'ud, and Ibn Abbas, and is attributed to Al-Hasan, Ibn Sirin, Shurayh, Ata, Mujahid, Al-Thawri, Abu Hanifa, and his companions. It is the current practice in major cities. The rationale is that since these heirs would equally bear any deficiency (casus aequitatis), they should equally receive the surplus. Furthermore, if the problem resulted in an increase (casus 'awl), the reduction would affect them all, so the return should likewise benefit them.
Supporting text
Ibn Mas'ud reportedly did not return the surplus to a granddaughter with a daughter, or to a consanguineal sister with a full sister, nor to a grandmother with a fixed-share heir. Ahmad reportedly did not return the surplus to a child with the mother, or to a grandfather with a fixed-share heir.