Riyad as-Salihin 17:118

'Uqbah bin 'Amir (May Allah be pleased with him) said:

The Messenger of Allah (ﷺ) said, "Avoid (entering a place) in which are women (uncovered or simply to mix with them in seclusion)." A man from the Ansar said, "Tell me about the brother of a woman's husband." He replied, "The brother of a woman's husband is death." [Al- Bukhari and Muslim] .