Standing on Laylat al-Qadr
مَنْ قَامَ لَيْلَةَ الْقَدْرِ إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ
Man qama laylata-l-qadri imanan wa-htisaban ghufira lahu ma taqaddama min dhanbih.
"Whoever stands in prayer on Laylat al-Qadr out of faith and seeking reward, his previous sins are forgiven."
Narrated by Abu Hurayrah. Sahih al-Bukhari 1901, Sahih Muslim 760
A short reflection
One night, better than a thousand months. The same two conditions hold. The Prophet ﷺ used to spend the last ten in seclusion, looking for it.