What is the ruling on the husband of the wife's sister entering upon her in the absence of her husband?

If the husband gives permission or does not object to strangers entering his home during his absence, there is no harm in that, provided that seclusion (khalwa), displaying adornment (zina), or speaking in a submissive manner are avoided. However, if he dislikes it, then it is not permissible, due to the Prophet’s saying: "And you have a right over them that they should not allow anyone you dislike to step on your beds," and this includes any person the husband dislikes entering his home.