What is the ruling on supplicating for a guardian (wali) who governs by other than what Allah has revealed?

Supplicating for the Muslim ruler, advising him, and assisting him are permissible, as long as he does not commit blatant disbelief. This is based on the Prophet's (peace be upon him) saying: "And that you advise those whom Allah has given authority over you." It is permissible to supplicate for a deviant ruler who is not a disbeliever, because he is the most in need of supplication, and with his righteousness, society becomes righteous.