Praise be to Allah.
There is no such thing in the hadeeth of the Prophet (peace and blessings of Allaah be upon him) as that which the questioner mentions, “Commerce is better than a salary.” The closest thing is the hadeeth, “Nine-tenths of provision is in trade,” which is a da’eef (weak) hadeeth that was classed as such by al-Albaani in Da’eef al-Jaami’, 2434.
What one of your friends has suggested to you, that the customers bring their own wine with them to your restaurant, is false according to sharee’ah. It is bad advice, whether it is intended to cause you harm or it comes from one who is ignorant and does not know the ruling of Allaah.
That is because you will be answerable to Allaah about your restaurant, and it is not permissible for you to allow sin to be committed in it. Drinking alcohol is haraam and no Muslim doubts that. It is a great evil, so how are you going to deal with this evil? The Prophet (peace and blessings of Allaah be upon 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 that it is wrong).” (Narrated by Muslim, 49).
Have you tried to change this evil by taking action, or by speaking out?
There is another issue.
It was narrated that Jaabir said: The Prophet (peace and blessings of Allaah be upon him) said: “Whoever believes in Allaah and the Last Day, let him not sit at a table at which alcohol is passed round.”
(Narrated by al-Tirmidhi, 2801. This hadeeth has corroborating reports which render it saheeh. It was classed as saheeh by al-Haafiz ibn Hajar in Fath al-Baari, 9/250).
Do not forget that this table belongs to you and is in your place. What is meant is not only sitting. Even if you are in the same place or the same restaurant, you are sharing with them in the sin, so how about if the place is your place?
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”
Ibn Katheer said: This means, if you commit the forbidden action after you have heard that it is forbidden, and you agree to sit with them in the place in which they are denying the Verses of Allaah and mocking them, and you approve of that, then you are joining with them in what they are doing. Hence Allaah says, “you would be like them” in sin, as it says in the hadeeth, “Whoever believes in Allaah and the Last Day, let him not sit at a table at which alcohol is passed round.”
(Tafseer Ibn Katheer, 1/567, 568)
And there is another issue:
What if a person were to say that he wants to open a hotel in order to make money, and someone were to advise him to let anyone bring a woman there to sleep with her, because this will attract customers! Would you agree with this advice? The answer is, No, definitely not.
The same applies to the one who told you that if you want to make money you have to let the customers bring their own wine with them. There is no difference. In both cases, you would not be offering wine or women, but you would be allowing people to commit haraam actions in front of your eyes in your place.
Based on that, it is haraam for you to allow anyone to bring something that Allaah has forbidden and drink it in your restaurant. Allaah says (interpretation of the meaning):
“And whosoever fears Allaah and keeps his duty to Him, He will make a way for him to get out (from every difficulty).
And He will provide him from (sources) he never could imagine”
So you should not be deceived by what people say when they tell you that you will not make any money unless you allow people to bring these haraam things into your restaurant. These people are not offering you sincere advice, or they want to offer advice but they are going about it the wrong way.
And Allaah knows best.