Is the treatment of a Muslim different from that of a disbeliever regarding assistance in sin, and why is it permissible to rent a house to a disbeliever despite knowing of their engagement in forbidden acts, while it is not permissible to rent it to a Muslim if it is highly probable that they will witness forbidden acts?

The treatment of a Muslim differs from that of a Dhimmi or Mu'ahid disbeliever. The disbeliever is allowed to practice what he believes to be permissible in his religion, even if it is forbidden in Islam, provided that he does not display it publicly among Muslims. This includes his invalid acts of worship, drinking alcohol, and eating pork, because he believes them to be lawful. However, he is prohibited from displaying these acts among Muslims. As for the Muslim, he is not allowed to commit these forbidden acts and is punished for them.

Therefore, it is permissible to rent a dwelling to a disbeliever, even if one knows he will practice forbidden acts therein, because he is allowed to do so. However, it is not permissible to rent a shop for selling alcohol or pork, because he is prohibited from displaying such acts among Muslims. As for renting a dwelling to a Muslim who is likely to practice forbidden acts, it is not permissible, because he is not allowed to commit these forbidden acts, and it is forbidden to assist him in them.