Why did Islam prohibit bequests to heirs?

A bequest to an heir is not permissible, based on the Prophet's (peace and blessings of Allah be upon him) saying: (Indeed, Allah has given every rightful person his due, so there is no bequest to an heir.) The wisdom behind this prohibition is to prevent an heir from taking more than his rightful share according to Islamic law, thereby transgressing Allah's boundaries in inheritance, which could lead to animosity and envy among the heirs. If a bequest to an heir were permissible, the determined shares of inheritance would be invalidated, and people would tamper with them.