Ok, suddenly the casino you're playing asks you for proof of income to be able to withdraw your winnings and to keep your account in good standing, your bankroll every month is $500 and you provide proof of salary that you are making $500 net every month, will they accept that proof will they accept that you are putting all your salary for gambling, will this violate the principle of gamble for fun, because you are working to gamble based on your proof income.
I think
they don't even have the right to prohibit you from gambling even though your money in gambling comes from your monthly salary, of course, this will be a bad habit if you play your monthly salary for gambling. But back to the point I mentioned (bold text). Then, I also wonder, on which site do you play? is this a physical casino? I also want to know more about this. But whatever it is, if what they are asking for is an obligation to withdraw money, like it or not you have to provide the data they ask for.