From Sahih Muslim (Hadith 5674):
Uqba b. `Amir reported Allah's Messenger (ﷺ) 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 (ﷺ) said: Husband's brother is like death
Reference: Muslim 5674