Allah says
وَلَهُنَّ الرُّبُعُ مِمَّا تَرَكْتُمْ إِن لَّمْ يَكُن لَّكُمْ وَلَدٌ ۚ فَإِن كَانَ لَكُمْ وَلَدٌ فَلَهُنَّ الثُّمُنُ مِمَّا تَرَكْتُم ۚ مِّن بَعْدِ وَصِيَّةٍ تُوصُونَ بِهَا أَوْ دَيْنٍ ۗ
(And for them is the fourth of what you leave, If you have no child, If you have a child, they shall have an eighth of what you leave, after a bequest you made or a debt)
1 - The amount of the wife's inheritance if the husband had a son
If the husband died and he had an inheriting descendant; as a son, and the son of the son, though descended, the daughter and the daughter of the son, and if descended, whether this was the heir from that wife or from another, the wife's share of the inheritance is one-eighth, And the evidence for that is the words of God - glory be to Him - in the decisive revelation: (If you have a child, they will have an eighth of what you leave).
2 - The amount of the wife's inheritance if the husband does not have a child
If the husband died and he did not have an inheriting descendant; whether male or female, the wife's share of the inheritance is one-fourth, and the evidence for that is the words of God - the Most High - in His Holy Book: (And for them is a fourth of what you leave, if you have no child.)
he amount of the wife's inheritance if the husband has more than one wife
If the deceased husband had more than one wife, the share does not increase by increasing them, rather, all his wives share a quarter or an eighth based on whether or not there is an inheriting descendant.
The Impediments to the wife's inheritance
The Islamic law stipulates that the wife has a share of her husband’s inheritance, however, there are obstacles that lead to non-inheritance between the spouses, and they are as follows:
A - The difference of religion
If the husband is a Muslim and the wife is not, then she does not inherit; for different religion, On the authority of Osama bin Zaid - may God be pleased with him - he said: The Messenger of God - may God’s prayers and peace be upon him - said: (The Muslim does not inherit the infidel, and the infidel does not inherit the Muslim) If the husband has a Muslim wife and another of the people of the Book, the Muslim woman takes her full share of the inheritance, nothing to write about; The difference in religion between them between the deceased husband.
the kill
If the wife deliberately kills her husband, she is deprived of inheritance, On the authority of Abdullah bin Amr - may God be pleased with him - he said: The Messenger of God - may God’s prayers and peace be upon him - said: (The murderer has nothing from the inheritance).
A major irrevocable divorce
If a man irrevocably divorces his wife, the right to inheritance is not proven to her unless it is proven that he divorced her during the illness of death intending to deprive her of her inheritance, In this case, she inherits from her husband, as for the revocable divorced woman, whether her divorce took place in the event of the husband’s health or illness, it inherits; Because revocable divorce does not cut off the marital rule as long as the waiting period remains.