Answered by Mufti Mohammed Tosir Miah
Question:
A cousin of mine lives in Nairobi where he’s running Hotel & Restaurant business. And you know that there are more non-Muslims in Nairobi and they can’t live without alcohol. And obviously my cousin (Zaid) is neither selling nor serving alcohol in his hotel/restaurant. Now if some customer brings alcohol and wine/beer glasses from outside to consume in Zaid’s premises during his/her stay in the hotel/restaurant without Zaid’s consent or knowledge, then will Zaid be responsible for this? That is; will he get sins? And will his income from such customer be Haraam? And if some customer asks for Zaid’s permission to consume alcohol in Zaid’s hotel/restaurant on condition that the customer will use his/her own glass, then can Zaid give him permission or not? If he refuses, then he’s afraid of losing many customers which will eventually result in a loss in his business. Please kindly advise me according to the shariah on what Zaid should do in the above situation.
Answer:
It will not be permissible for you to allow anyone to drink alcohol on your premises even though they may be bringing their own glasses.
Allah enjoins the Muslim to denounce evil when he sees it or knows of it taking place.
Saaiduna Abu Saeed Al Khudri 
narrates that the Prophet of Allah 
has 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.” (Sahih Muslim)
If in your absence they brought the alcohol onto the premises and started drinking it then as you were unaware of they were doing it will not affect your rizq and income in an unlawful way.
Allah 
says in the Holy Qur’an:
“Allah does not subject a soul except with that within its capacity.” (Surah Baqarah v.286)
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham