‘Avoid women’. One man asked, ‘Yā Rasūlallāĥ صَلَّى اللهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم! What about the brother-in-law?’ He صَلَّى اللهُ تَعَالٰى عَلَيْهِ وَاٰلِهٖ وَسَلَّم answered, ‘The brother-in-law is death.’ (Ṣaḥīḥ Bukhārī, vol. 3, pp. 472, Ḥadīš 5232)

A brother-in-law confronting his sister-in-law is like the one confronting death because there is a higher risk of indecency here. Muftī-e-A’ẓam Pakistan, Waqār-e-Millat, Maulānā Waqāruddīn  عَـلَيْهِ رَحْـمَةُ الـلّٰـهِ الۡـمُبِیْن says, ‘It is necessary for her to observe ‘veil’ excluding her face, palms, heels, feet and ankles; with all men that are non-Maḥram); she should also avoid revealing her beauty, jewellery and dress to them.’ (Waqār-ul-Fatāwā, vol. 3, pp. 101)

One narration states, ‘If any man casts a lustful glance at the beauty of a non-Maḥram woman, then on the Day of Judgement, molten lead will be poured into his eyes’. (Ĥidāyaĥ, vol. 2, pp. 368)

One’s sister-in-law is definitely a non-Maḥram woman. Any brother-in-law who has deliberately and lustfully been looking at, behaving casually towards, or joking around with his sister-in-law, must fear Divine punishment and instantly repent without delaying a single millisecond. If a woman refers to her brother-in-law as ‘younger brother’ or ‘older brother’ then this does not make it permissible for them to see each other and have an informal relationship. In fact, this kind of informal chit-chat removes any formalities and brings them close, which results in the brother-in-law and sister-in-law falling even deeper into the ditch of sins, such as looking at each other, casual behaviour, joking, laughing etc. Informal conversation between a woman and her brother-in-law sounds a constant alarm signifying extreme danger.

May Allah عَزَّوَجَلَّ make these words penetrate the heart.