The Essence
While Al-Ghaffar forgives sins repeatedly, Al-Ghafoor is the One who completely forgives sins of immense magnitude. He not only pardons the sin but covers it, acting as if it never happened, regardless of its size.
In the Quran
نَبِّئْ عِبَادِي أَنِّي أَنَا الْغَفُورُ الرَّحِيمُ
"[O Muhammad], inform My servants that it is I who am the Forgiving (Al-Ghafoor), the Merciful. (Surah Al-Hijr 15:49)"
In Your Duas
رَبِّ اغْفِرْ لِي وَتُبْ عَلَيَّ إِنَّكَ أَنْتَ التَّوَّابُ الْغَفُورُ
"My Lord, forgive me and accept my repentance. Indeed, You are the Accepting of repentance, the Forgiving."
— Sunan Ibn Majah 3814