Ramadan

مَنْ صَامَ رَمَضَانَ إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ وَمَنْ قَامَ لَيْلَةَ الْقَدْرِ إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ

Whoever fasts the month of Ramadan due to faith and seeking reward, his previous sins will be forgiven. Whoever stands in prayer during the Night of Decree due to faith and seeking reward, his previous sins will be forgiven.

Source: Ṣaḥīḥ al-Bukhārī 1901, Grade: Muttafaqun Alayhi