What is the ruling on supplicating against someone who insults the Divine Being, and supplicating for their guidance?

Whoever curses Allah the Almighty is an infidel (kafir). It is permissible to supplicate against a stubborn infidel. It is also permissible to supplicate for their guidance, especially if there is hope for their conversion to Islam. The Prophet, peace and blessings be upon him, used to say to the Jews when they sneezed: "May Allah guide you and rectify your affairs."