What is the religious ruling if a person rents out an apartment, but it is probable that the tenant deposits his money in an interest-based bank and pays the rent from it, or is an alcoholic, or engages in any unlawful act, while the landlord is unaware of this?

If the Sacred Law permits dealing with a non-Muslim under certain conditions, then it is all the more permissible to deal with a Muslim, even if he is a sinner, unless it is known that he is renting the premises for the purpose of committing a sin. As for the ruling on the rent, if the tenant's earnings are entirely lawful or are dubious, there is no harm in taking it. If some of his money is unlawful and some is lawful, it is permissible to take the rent from him.