The widower's share in the wife's property in Islam is fixed and prescribed and vice-versa. A widower inherits one-half (i.e., 1/2) fixed or prescribed division from the property of the deceased Wife's assets if no children or no grandchildren how low soever survive (i.e., in the absence of lineal descendants); otherwise, inherit one-fourth (i.e., 1/4) from Wife's property as stipulated in the Holy Quran 4:12.
Surviving spouse does not inherit residue as Residuary. The widower's share can vary in certain conditions due to the decrease or increase of total shares under the Radd and Awal (or Aul) scenario.
No Hajb (i.e., blocking or exclusion) rules are applicable for spouses and do not block any legal heirs from taking an inheritance and vice-versa.
The widower inherits from his wife only if he is married as per a Muslim ceremony called "Nikah." The surviving spouse does not inherit under shariah if he is only married legally.
A woman's property can be inherited by her spouse, children (or grandchildren), and parents (or grandparents) as primary heirs. These are the legal heirs after the death of a married woman in Islam. Refer to "Sharer and Residuary" to learn more.
The husband also can own lifetime gifts (i.e., Hiba) from the Wife's property without any classification or restrictions.