If he allows people who bring alcohol with them to drink it in his restaurant, is he sinning?
Question

                My food in restaurant is halal I cook only halal food and serve. The restaurant I bought from kufr and the city transferred liquor license to my name. I do not sell alcohol but my customers bring in bottles wine for their dinner, which is allowed city ordinance. May I allow them to do this, or should I turn them away? They do not misbehaving or bother other customers, and when license expires I will not be of renewing it.
Praise be to Allah.
    (a)

    The owner of the restaurant is responsible, according to 
    sharee’ah, for what happens in his restaurant of sins that he could stop or 
    prevent from happening in the first place. The prohibition of alcohol is 
    proven in the Qur'aan and Sunnah and according to scholarly consensus. The 
    Prophet  (peace and blessings of Allaah be upon him) cursed ten people 
    with regard to alcohol, not just the one who drinks it. 

    It was narrated that Anas ibn Maalik (may Allaah be pleased 
    with him) said: The Messenger of Allaah (peace and blessings of Allaah be 
    upon him) cursed ten types of people with regard to alcohol: the one who 
    presses (the grapes, etc), the one for whom that is done, the one who drinks 
    it, the one who carries it, the one to whom it is carried, the one who 
    offers it, the one who sells it, the one who consumes its price, the one who 
    buys it and the one for whom it is bought. 

    Narrated by al-Tirmidhi (1259) and Ibn Majaah (3381); classed 
    as saheeh by al-Albaani in Saheeh al-Tirmidhi. 

    This proves that the sin includes everyone who contributed 
    towards its presence, so that it may be drunk at the end. 

    (b) 

    The one who sits in a place where Allaah is denied and where 
    evil actions and sins are committed is a participant with them in that sin, 
    if he is able to change the evil but does not do so, or he is able to leave 
    that gathering but does not do so. Allaah says (interpretation of the 
    meaning):

    “And it has already been revealed to you in the Book (this 
    Qur’aan) that when you hear the Verses of Allaah being denied and mocked at, 
    then sit not with them, until they engage in a talk other than that; (but if 
    you stayed with them) certainly in that case you would be like them. Surely, 
    Allaah will collect the hypocrites and disbelievers all together in Hell”

    [al-Nisa’ 4:140]. 

    Ibn Katheer (may Allaah have mercy on him) said: 

    i.e., if you commit sin after it has reached you, and you 
    agree to sit with them in a place in which the verses of Allaah are being 
    denied and mocked and belittled, and you approve of them doing that, then 
    you have a share with them in what they are doing. Hence Allaah says “certainly 
    in that case you would be like them” i.e., in sin, as it says in the 
    hadeeth: “Whoever believes in Allaah and the Last Day, let him not sit at a 
    table where alcohol is being passed around.” End quote. 

    Tafseer Ibn Katheer (2/435). 

    (c)

    Allaah enjoins the Muslim to denounce evil when he sees it or 
    knows of it taking place. So how can this coincide with allowing those 
    customers to drink alcohol in your restaurant? 

    It was narrated that Abu Sa’eed al-Khudri (may Allaah be 
    pleased with him) said: “Whoever among you sees an evil action, let him 
    change it with his hand (by taking action); if he cannot, then with his 
    tongue (by speaking out); and if he cannot, then with his heart (by hating 
    it and feeling it is wrong), and that is the weakest of faith.”

    Narrated by Muslim (49). 

    (d)

    Another of the attributes of the slaves of the Most Merciful 
    is that which Allaah says of them in the verse (interpretation of the 
    meaning):

    “And those who do not bear witness to falsehood, and if 
    they pass by some evil play or evil talk, they pass by it with dignity”

    [al-Furqaan 25:72]. 

    According to some scholars – such as Imam al-Zuhri – what is 
    meant by falsehood is drinking alcohol. 

    See: Tafseer Ibn Katheer (6/130). 

    Based on that: 

    You should put a stop to this by not allowing anyone to drink 
    alcohol in your restaurant, otherwise you will be taking upon yourself the 
    sin of those drinkers. Do not hesitate about this matter, and you will see 
    the effect of that in your religious commitment and in your provision 
    (rizq), if you seek reward from Allaah in this matter. 

    And Allaah knows best.