Wrongfully judging a person to be an apostate because he went out with a girl who was unveiled
Question

                What is the ruling on a person who says to someone, "You are an apostate from Islam" because he goes with a girl who is unveiled and wears makeup?.
Praise be to Allah.
    Firstly: 

    It is not permissible for a Muslim to use the word kaafir 
    lightly, because judging a Muslim who believes in Tawheed to be a kaafir is 
    a major sin. Muslim (60) narrated from 'Abd-Allaah ibn 'Umar that the 
    Messenger of Allaah  (peace and blessings of Allaah be upon him) 
    said: "Any man who says to his 
    brother, 'O kaafir,' if this description fits him, then he is a kaafir, 
    otherwise it will come back on him (the one who said it)." 

    Al-Bukhaari (6054) narrated from Abu Dharr (may Allaah be 
    pleased with him) that he heard the Prophet  (peace and blessings of 
    Allaah be upon him) say: "No man accuses another of being immoral or of 
    being a kaafir but it will come back on him if his companion is not like 
    that." 

    Secondly: 

    The one who wants to denounce an evil action or to exhort a 
    sinner should do that in a kind and gentle manner, because this is more 
    likely to make his words acceptable and effective. It was narrated from 
    'Aa'ishah, the wife of the Prophet  (peace and blessings of Allaah be 
    upon him) that the Messenger of Allaah  (peace and blessings of Allaah 
    be upon him) said: "Allaah is Kind and loves kindness, and He gives (reward) 
    for kindness that He does not give for harshness and He does not give for 
    anything else. 

    Al-Nawawi said: 

    This hadeeth points to the virtue of kindness and encourages 
    us to adopt this attitude; and it condemns harshness. Kindness is the cause 
    of all goodness. Al-Qaadi said: What this means is that goals may be 
    achieved by means of kindness that cannot be achieved by anything else. 

    With regard to uttering words such as kaafir (disbeliever), 
    faasiq (immoral person), murtadd (apostate), etc, this may be a cause of the 
    person being put off and persisting in his sin, and not accepting the 
    truth. 

    Al-Haafiz said in his commentary on the hadeeth of Abu Dharr 
    mentioned above: 

    This shows that if a person says to another, "You are a 
    faasiq (immoral person)" or "You are a kaafir", and that is not the case, 
    then he is the one who deserves to be described in that manner. If the 
    person is as described, it does not necessarily mean that the one who called 
    him that is free of sin. If the intention is to advise him or someone else 
    by referring to his situation, it is permissible, but if the intention is to 
    expose and shame him, and and to hurt him, then it is not permissible, 
    because we are commanded to conceal people's faults and teach then and 
    advise then in a manner that is better. As far as a person is able to 
    achieve that in a kind manner, it is not permissible for him to do it in a 
    harsh manner, because that may make him stubborn and cause him to persist in 
    that action, as is the nature of many people.  

    Thirdly: 

    Going with a girl who is unveiled and wears makeup is not 
    kufr, rather it is a sin because it is one of the means that lead to immoral 
    actions. But he should advise this person who has gone with a girl who is 
    unveiled and wears makeup, so that Allaah may guide him thereby.