Is it permissible for the husband’s brother to take his brother’s wife to the doctor?
Question

                Is it permissible for the husband’s brother to take his brother’s wife to the doctor, if his brother is not there, or if he cannot be there, and the hospital is in the same city?.
Praise be to Allah.
    It is not permissible for the wife to travel in a car alone 
    with her husband’s brother, because that comes under the heading of khulwah 
    (being alone with a member of the opposite sex) which the Messenger  
    (peace and blessings of Allaah be upon him) warned against when he said: 
    “Beware of entering upon women.” They said: “O Messenger of Allaah, what 
    about the in-law?” He said: “The in-law is death.” Narrated by al-Bukhaari 
    and Muslim. 

    What do you understand from these words? Is it forbidden or 
    allowed? Undoubtedly what is meant is that it is forbidden and not allowed. 
    So it is not permissible for a man to be alone with his brother’s wife, 
    either in a car or in the house. Worse than that is what some people do when 
    a guest comes when the man is at work, and there is no one in the house 
    except his wife, then she opens the door to him and he goes in and waits for 
    the owner of the house to come home. The point is that it is not permissible 
    for any woman to be alone with any man (i.e., non mahrams) even if he is one 
    of her husband’s relatives or one of her relatives or neighbours, unless she 
    has a mahram with her, whether that is in her home town or when travelling. 
    It should also be noted that it is haraam for her to travel even if there is 
    no khulwah, if she does not have a mahram with her, because of the hadeeth 
    of Ibn ‘Abbaas (may Allaah be pleased with him) which is narrated in 
    al-Saheehayn. He said: I heard the Prophet  (peace and blessings of 
    Allaah be upon him) delivered a khutbah and said: “No man should be alone 
    with a woman unless there is a mahram with her, and no woman should travel 
    without a mahram.”