From Sahih Bukhari (Hadith 5232):
Narrated `Uqba bin 'Amir:Allah's Messenger (ﷺ) said, "Beware of entering upon the ladies." A man from the Ansar said, "Allah's Apostle! What about Al-Hamu the in-laws of the wife (the brothers of her husband or his nephews etc.)?" The Prophet (ﷺ) replied: The in-laws of the wife are death itself
Reference: Bukhari 5232