Du'a using Allah's Name Al-Qahhar

اللَّهُمَّ يَا قَهَّارُ اقْهَرْ مَنْ ظَلَمَنَا

Allahumma ya Qahhaaru iqhar man dhalamana

O Allah, The All-Prevailing, prevail over those who have wronged us.

A general supplication, not a narration from the Prophet (peace be upon him).