Is there proof that it is forbidden to deceive the ruler?

Obedience to those in authority is obligatory as long as they do not command disobedience. If they command disobedience, then there is no listening or obedience to them in that matter. It is permissible for the ruler to restrict what is otherwise permissible if there is a public interest in doing so, and it is then not permissible to disobey him. The proof for the obligation of obedience in what is right is Allah's saying: "O you who have believed, obey Allah and obey the Messenger and those in authority among you. And if you disagree over anything, refer it to Allah and the Messenger, if you should believe in Allah and the Last Day. That is the best [way] and best in result" (An-Nisa:59), and the Prophet's (peace be upon him) saying: "Obedience is only in what is right." Obedience to him is obligatory in what is right, even if he is not upright or is unjust. However, if the ruler's commands do not involve a public interest, then adherence to them is not obligatory, and it is permissible to disobey them. If a Muslim fears that disobedience will lead to humiliation and harm, then he should not debase himself.