Source: Fatāwā ʿIlmiyyah (Tawḍīḥ al-Aḥkām), Vol. 2, p. 509
Question:
Is the sister-in-law considered a non-maḥram, and is it necessary to observe ḥijāb from her?
Answer:
Al-ḥamdu lillāh, waṣ-ṣalātu was-salāmu ʿalā Rasūlillāh, ammā baʿd!
From the general Islamic texts, it is evident that a sister-in-law is a non-maḥram for a man; therefore, it is obligatory to observe ḥijāb from her.
ھذا ما عندي والله أعلم بالصواب
