Assalamualaikum Wa Rahmatullahi Wa Barakathu.
What is the ruling on adultery with one’s wife’s sister?
In the name of Allah, Most Compassionate, Most Merciful,
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
Indeed, committing adultery is one of the major sins in Islam and a despicable act in the eyes of Allah Ta’alā. Allah Ta’alā says:
وَلَا تَقْرَبُوا الزِّنَا إِنَّهُ كَانَ فَاحِشَةً وَسَاءَ سَبِيلًا (سورة الاسراء: 32)
Translation: “And do not go close to adultery. Indeed, it is ever an immorality and it is an evil way.”
Furthermore, Rasulullah (Sallallahu Alaihi Wasallam) advised one to be very cautious around one’s in-laws. See the following Hadith:
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 ” (صحيح مسلم: 2172)
Translation: Uqba bin Amir reported Allah’s Messenger (Sallallahu Alaihi Wasallam) as saying: Beware of getting, into the houses and meeting women (in seclusion). A person from the Ansar said: Allah’s Messenger, what about husband’s brother, whereupon he (Sallallahu Alaihi Wasallam) said: Husband’s brother is like death. (Saheeh Muslim: 2172)
Nevertheless, the rulings pertaining to committing adultery with one’s sister in law are the same as committing adultery with a common woman. In an Islamic country, an unmarried individual found guilty of adultery would receive 100 lashes and a married individual found guilty of adultery would be punished by stoning to death.[i]