Du'a using Allah's Name Al-Ghaffar

اللَّهُمَّ يَا غَفَّارُ اغْفِرْ ذُنُوبَنَا

Allahumma ya Ghaffaru ighfir dhunoobana

O Allah, The Great Forgiver, forgive our sins.

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