Pardah for a Brother-in-Law

Q: Is it necessary for a woman to observe pardah with her brother-in-law?

A: Rasoolullah (sallallahu alayhi wasallam) said: The brother-in-law is death (narrated by Imam Tirmizhi). The reasons for such a stern warning are: a) Sister-in-law and brother-in-law sometimes live in the same house, so there is often intermingling. b) Because of such frequent intermingling people tend to relax the law of pardah. c) If brother-in-law gets involved with sister in law, the repercussions of this zinaa is far worse than committing zina with an outsider, and eventually leads to severing of family ties. Sister-in-law and brother-in-law are not mehrams; they are total strangers, so hijaab is wajib between the two.