He owns an café in which men and women mix
Question

                A man owns a high-quality café which has a mixed clientele of men and women. He feels uneasy because of this mixing and fears that the income from this café may come under the heading of things which are forbidden or are doubtful and therefore disallowed in sharee’ah, even though he has told his employees not to sell anything that is forbidden in sharee’ah, such as cigarettes, and he has forbidden his customers to do anything that goes against Islamic etiquette. We would like you to please shed some light on this issue by quoting some verses of Qur’aan and ahaadeeth of the Prophet (peace and blessings of Allaah be upon him), so that we may find some peace of mind and avoid falling into sin, and we may meet our Lord when He is pleased with us. We hope that the answer will be detailed.
Praise be to Allah.
    The owner of this café has done well by refusing to sell 
    forbidden substances in his café, such as refusing to sell cigarettes and 
    refusing to allow people to do things that go against Islamic etiquette. May 
    Allaah reward him with good. 

    But it remains for him to forbid mixing, because of the evil 
    and temptation that it involves. The Qur’aan and Sunnah indicate that mixing 
    is haraam. For example: 

    Allaah says (interpretation of the meaning): 

    “And when you ask (his wives) for anything you want, ask 
    them from behind a screen, that is purer for your hearts and for their 
    hearts”

    [al-Ahzaab 33:53]

    Ibn Katheer (may Allaah have mercy on him) said, commenting 
    on this verse: i.e., just as it is forbidden for you to enter upon them, it 
    is also forbidden for you to look at them at all; even if one of you has a 
    need to ask them for anything, he should not look at them or ask of them 
    except from behind a screen. 

    Al-Qurtubi (may Allaah have mercy on him) said: This verse 
    indicates that Allaah has given permission to ask of them from behind a 
    screen in the case of necessity, or when consulting them about some matter. 
    This meaning includes all women, because the basic principle of sharee’ah is 
    that the whole of a woman is ‘awrah. 

    And Allaah says (interpretation of the meaning): 

    “O wives of the Prophet! You are not like any other women. 
    If you keep your duty (to Allaah), then be not soft in speech, lest he in 
    whose heart is a disease (of hypocrisy, or evil desire for adultery) should 
    be moved with desire, but speak in an honourable manner”

    [al-Ahzaab 33:32]

    If there is this warning against being soft of speech lest 
    the one in whose heart is a disease be moved with desire, then what about 
    men sitting with women who are clothed yet naked, who go astray and lead 
    others astray, chatting and laughing together, and looking at one another? 
    What fitnah can be greater than that? What heart can remain free of sickness 
    when this is the case? 

    The Prophet  (peace and blessings of Allaah be upon him) 
    took care to prevent men mixing with women even in the dearest spots on 
    earth to Allaah, namely the mosques, when he separated the rows of men and 
    women, and he stayed for a while after saying the salaam so that the women 
    could depart, and he designated a door of the mosque specifically for women. 
    The evidence for that is as flows: 

    1 – It was narrated that Umm Salamah (may Allaah be pleased 
    with her) said: When the Messenger of Allaah  (peace and blessings of 
    Allaah be upon him) had said the salaam, the women would get up and leave 
    when they had said the salaam, and he would stay for a while before getting 
    up to leave. Ibn Shihaab said: I think – and Allaah knows best – that he 
    stayed a while so that the women could disperse before the men got up to 
    leave. Narrated by al-Bukhaari, no. 793. 

    2 – It was narrated that Ibn ‘Umar (may Allaah be pleased 
    with him) said: The Messenger of Allaah  (peace and blessings of Allaah 
    be upon him) said: “Why don’t we leave this door for the women?” Naafi’ 
    said: Ibn ‘Umar never entered through that door until he died. Narrated by 
    Abu Dawood, 462; classed as saheeh by al-Albaani in Saheeh Abi Dawood. 

    3 – It was narrated that Abu Hurayrah (may Allaah be pleased 
    with him) said: The Prophet  (peace and blessings of Allaah be upon him) 
    said: “The best rows for men are the first ones and the worst are the last, 
    and the best rows for women are the last ones and the worst are the first.” 
    Narrated by Muslim, 664. 

    This is among the greatest evidence that Islam forbids 
    mixing. The further away the men are from the women’s rows the better, and 
    the further away the women are from the men’s rows the better. 

    If these precautions are to be taken in the mosque which is a 
    pure place of worship, then taking them in other places is undoubtedly more 
    important. 

    4 – It was narrated from Abu Usayd al-Ansaari that he heard 
    the Messenger of Allaah  (peace and blessings of Allaah be upon him) 
    say, when he was outside the mosque and the men were mixing with the women 
    in the road. The Messenger of Allaah  (peace and blessings of Allaah be 
    upon him) said to the women: “Move aside, for you have no right to walk in 
    the middle of the road; you should walk at the sides of the road.” Then a 
    woman would walk so close to the walls that her garment would catch on the 
    wall because she walked so close to it.” Narrated by Abu Dawood, 5272; 
    classed as hasan by al-Albaani in Saheeh Abi Dawood. 

    For more details on the dangers of mixing, please see the 
    answer to question no. 1200. 

    Since mixing is haraam, the owner of this café is committing 
    sin by allowing it and refraining from denouncing it, and by helping these 
    people to commit sin by providing a place for them where they can disobey 
    Allaah. 

    What he has to do is to fear Allaah and not help to spread 
    evil and corruption among the believers. He should be keen to make his food 
    good (i.e., from halaal sources), for “every body that is nourished on 
    haraam, the Fire is more befitting for it,” as the Prophet  (peace and 
    blessings of Allaah be upon him) said. Narrated by al-Tabaraani and Abu 
    Na’eem from Abu Bakr; classed as saheeh by al-Albaani in Saheeh al-Jaami’, 
    no. 4519. 

    Another version was narrated from Ka’b ibn ‘Ajrah: “No flesh 
    grows that is nourished by haraam but the Fire is more befitting for it.”  

    If he can prevent mixing, then this is what he must do, or 
    else he can restrict the café to men only. Otherwise he should look for 
    other, permissible work. Whoever gives up a thing for the sake of Allaah, 
    Allaah will compensate him with something better than it. 

    “And whosoever fears Allaah and keeps his duty to Him, He 
    will make a way for him to get out (from every difficulty).

    3. And He will provide him from (sources) he never could 
    imagine”

    [al-Talaaq 65:2-3]

    And Allaah knows best.