Fifthly, the newly created heirs inherit the specified shares along with customary heirs, and not to their exclusion. After allotting the specific shares to the newly created heirs, who are called sharers, whatever is left (residue) and the scheme is so laid down that something is usually left, goes to the customary heirs who are called residuary. It is necessary to notice that the Koran did not create a new structure of law of succession, but merely amended and modified the customary law of succession so as to bring it in conformity with the Islamic philosophy. When the Koran enumerates certain heirs and allots specific shares to them, it does not mean that those who are not enumerated do not get any share. For instance, husband, wife, father, true grandfather, daughter, son’s daughter, sister and uterine brother are the Koranic heirs, but this does not mean that son or brother do not take anything in the inheritance. They continue to be heirs (they were heirs under customary law) and take their shares. What has happened is this that those persons were not heirs under the customary law have been made heirs (called shares of the Koranic heirs) and specific shares have been allotted to them.
For instance, if A, a Muslim, dies leaving behind a widow, W and two sons S and S then W will take one-eighth as her specified share and S and S will take the residue, i.e., seven-eighth. This super-imposition of the Koranic principles on the customary law of inheritance has led to divergence of opinion among the Shias and the Sunnis, resulting in the propagation of two different rules of inheritance.
According to Tayabji, the fundamental difference between the Shia and the Sunni law of inheritance are: (i) The Hanafis allow the framework or principles of the pre-Islamic customs to stand; they develop or alter those rules in the specific manner mentioned in the Koran, and by the Prophet. (ii) The Shias deduce certain principles, which they hold to underlie the amendments expressed in the Koran and fuse the principles so deduced with the principles underlying the pre-existing customary law, and thus raise up a completely altered set of principles and rules derived from them. Certain females are specially added in the Islamic scheme of succession, i.e.
, the sharers. Any custom to exclude them from inheritance has to be proved.