What are the most powerful answered supplications (duas) reported from the Messenger of Allah (peace be upon him) that an oppressed person can use to supplicate against their oppressor, and is the Messenger's supplication against the people of Ta'if among the most severe, and what is its correct text?

It is permissible for the wronged to supplicate against their oppressor without transgressing, but their patience and seeking reward from Allah are better and greater, for the supplication of the wronged is answered. There is no specific supplication mentioned for an oppressor, and the wronged person may choose what suits their grievance. The Prophet (peace and blessings be upon him) did not supplicate against the people of Ta'if, and he used to say: "Indeed, I was not sent as a curser, but rather I was sent as a mercy."