Question Summary:
There is a common perception that the brtoher of the husband is “death”.

Question Detail:

There is a common perception that the brtoher of the husband is "death". However, the husband of the sister is generally not viewed in the same category since4 the wife cannot marry her sisters husband while she is in his nikah. Therefore, on many occassions, the wife will argue that her sisters husband is like a mahram, and not in the same category as the husbands brother. Please advise

Answer :

The following Hadīth is narrated in Sahīh Bukharī,
 
عَنْ عُقْبَةَ بْنِ عَامِرٍ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ  إِيَّاكُمْ وَالدُّخُولَ عَلَى النِّسَاءِ  فَقَالَ رَجُلٌ مِنَ الأَنْصَارِ يَا رَسُولَ اللَّهِ أَفَرَأَيْتَ الْحَمْوَ . قَالَ  الْحَمْوُ الْمَوْتُ (البخاري ج 6 ص 194 , دار الفكر)
 
‘Uqbah ibn ‘Āmir رضى الله عنه narrates that Rasūlullah صلى الله عليه و سلم said, “Beware of intermingling with women (in isolation)” then a man from the Ansār said, “O Rasūlullah, what about the brother-in-law (and other male in-laws)?” He صلى الله عليه و سلم replied, “The in-laws are death.”
 
From the beginning of this Hadīth, we learn that Rasūlullah صلى الله عليه و سلم prohibited any type isolation and intermingling between any non-Mahram men and women; thus, the prohibition is not restricted to certain relatives or people. It was only after the Sahābi asked Nabi صلى الله عليه و سلم about the brother in-law that Nabi صلى الله عليه و سلم specifically mentioned it. The commentators of Hadīth mention that the reason why Rasūlullah صلى الله عليه و سلم used such severe warnings in respect to a brother in-law is that people are generally negligent and careless in this regard. Thus, since the same negligence and carelessness exists in regards to the husband’s brother also exists in the wife’s sister; the same severe warning would apply to them. Furthermore, neither the husband’s brother is a Mahram nor is the wife’s sister. A Mahram according to the Sharī‘ah is such a person whom one can never marry. In the case of the brother in-law or sister in-law, it will be permissible to marry them after terminating the Nikah with the first husband or wife. They are in the same category in regards to their status of being non-Mahram. Thus, one should be equally as cautious in regards to the wife’s sister as the husband’s brother.
 
And Allah knows best
Ml. Yusuf bin Yaqub,
Student Darul Iftaa
Checked and Approved by:
Muhammed Zakariyya Desai,
Assistant Mufti
 Darul Iftaa, Madrassah In'aamiyyah