Abu Hurairah narrated that The Messenger of Allah (ﷺ) said:

“Whoever prays during the night in Ramadan out of sincere faith and seeking its reward from Allah, will have all of his previous sins forgiven." Agreed upon.

عَنْ أَبِي هُرَيْرَةَ ‏- رضى الله عنه ‏- أَنَّ رَسُولَ اَللَّهِ ‏- صلى الله عليه وسلم ‏-قَالَ: { مَنْ قَامَ رَمَضَانَ إِيمَانًا وَاحْتِسَابًا, غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ } مُتَّفَقٌ عَلَيْهِ [1]‏ .‏