رَبَّنَا أَتْمِمْ لَنَا نُورَنَا وَاغْفِرْ لَنَا ۖ إِنَّكَ عَلَىٰ كُلِّ شَيْءٍ قَدِيرٌ.
Our Lord, perfect for us our light and forgive us. Indeed, You are over all things competent.
Rabbana atmim lana nurana waghfir lana innaka ala kulli shay’in Qadir.
Scholars state that the Believers will utter these words on Judgment Day when they see the light of the hypocrites being extinguished. Because hypocrites only falsely declare their faith without ever truly believing, they live this life and benefit from the light of the Believers without having the light of faith themselves. This reality will be exposed on Judgment Day, and their borrowed light will abandon them and leave them in darkness. Hence, the Believers ask Allah to complete and perfect their light for them, and to forgive their sins. -Ibn Katheer.