What happens to the surplus when heirs with fixed shares do not exhaust the estate, according to Zayd ibn Thabit and his followers?
Chapter on the Roots of Inheritance Shares that Increase (Awl)
Al-Mughni
Book of Inheritance Shares (Farā'id)
Primary text
Zayd ibn Thabit, along with Malik, Al-Awza'i, and Al-Shafi'i, held that the surplus remaining after fixed-share heirs is returned to the public treasury (*bayt al-mal*), and no heir receives more than their stipulated fixed share. The evidence cited is the verse concerning the sister: {For her is half of what she leaves} [Quran 4:176], implying her share is fixed and cannot be increased beyond that, similar to the spouse. Furthermore, the basis for return relies on kinship, and the spouse is excluded from the definition of *dhu rahm* who merits the return over the public treasury.
Supporting text
The counter-argument maintains that the heirs entitled to the return are *dhu arham*, and by virtue of their closer relationship to the deceased, they are prioritized over the public treasury, which belongs to all Muslims and non-relatives. The verse stating the sister's half share does not preclude her receiving an increase via another title, analogous to how the father receives a sixth alongside the daughter, or how the husband might receive more if he is also a paternal cousin or a freed master.