What is the ruling on adultery with one's wife's sister?

In the Name of Allah, the Most Gracious, the 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:

Translation: “And do not go close to adultery. Indeed, it is ever an immorality and it is an evil way.”

(Surah Al-Isra:32)

Furthermore, Rasulullah (Sallallahu Alaihi Wasallam) advised one to be very cautious around one’s in-laws. See the following Hadith:

‏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.[1]

And Allah Ta’āla Knows Best

Student Darul Iftaa

Checked and Approved by,
Mufti Ebrahim Desai.