In ancient period, the weak, especially orphan Childs and Women among the Arab and non Arabian Nations was the victim of oppression and torture all the times. It would not accept any right of them and though it would accept, yet no one was the ability to take that from the men. It was the rules of Arab that who can ride horses, able to face enemies and have the power and capacity looted their money and wealth, can only be qualified for the successor. As the women and children are weak, they were not considered under that rule. Qur’an pays back to this class their proper right.
Some Muslim named Aaos ibn Sabet died leaving his wife, two daughter and a under aged boy. According to the conventional law, two of his cousin took possession of his property. Then the wife of Aaos fell in a great distress with his son and two daughters deprived from her husband’s property. So she proposed to those cousins whom occupied the property of her husband, to marry her two daughters, so that she can be relief of their thought. But this proposal was not accepted. Then Aaos’s wife came to Muhammd and raised a complaint describing her conditions and the rootlessness, deprivation of her children. But Muhammad took time to give her a decision as there were no verses yet sent in this regard. Then the following verses of Qur’an with the laws of inheritance sent down-
For men is a share of what the parents and close relatives leave, and for women is a share of what the parents and close relatives leave, be it little or much- an obligatory share.(4:7)
Allah instructs you concerning your children: for the male, what is equal to the share of two females. But if there are (only) daughters, two or more, for them is two thirds of one's estate. And if there is only one, for her is half. And for one's parents, to each one of them is a sixth of his estate if he left children. But if he had no children and the parents (alone) inherit from him, then for his mother is one third. And if he had brothers (or sisters), for his mother is a sixth, after any bequest he (may have) made or debt. Your parents or your children- you know not which of them are nearest to you in benefit. (These shares are) an obligation (imposed) by Allah. Indeed, Allah is ever Knowing and Wise.
And for you is half of what your wives leave if they have no child. But if they have a child, for you is one fourth of what they leave, after any bequest they (may have) made or debt. And for the wives is one fourth if you leave no child. But if you leave a child, then for them is an eighth of what you leave, after any bequest you (may have) made or debt. And if a man or woman leaves neither ascendants nor descendants but has a brother or a sister, then for each one of them is a sixth. But if they are more than two, they share a third, after any bequest which was made or debt, as long as there is no detriment (caused). (This is) an ordinance from Allah, and Allah is Knowing and Forbearing.(4:11-12)
They request from you a (legal) ruling. Say, “Allah gives you a ruling concerning one having neither descendants nor ascendants (as heirs)." If a man dies, leaving no child but (only) a sister, she will have half of what he left. And he inherits from her if she (dies and) has no child. But if there are two sisters (or more), they will have two-thirds of what he left. If there are both brothers and sisters, the male will have the share of two females. Allah makes clear to you (His law), lest you go astray. And Allah is Knowing of all things.(4:176)
After revealed this Muhammad gives one eighth of the total land of Aaos to his wife and the rest distribute to his children in such that the son gets half and the girls equally to the half of the son. On the other hand, cousin of Aaos were not closer than that of his children, so they are deprived.