He who prayed on the Lailat-ul-Qadr (the Majestic Night) knowing that it is (the same night). I (believe) that he (the Prophet also) said: (He who does) it with faith and seeking reward (from Allah), his sins would be forgiven.
عَنِ النَّبِيِّ ﷺ قَالَ مَنْ يَقُمْ لَيْلَةَ الْقَدْرِ فَيُوَافِقُهَا أُرَاهُ قَالَ إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ
Messenger of Allah ﷺ said, "Whoever establishes the prayers on the night of Qadr out of sincere faith and hoping to attain Allah's rewards (not to show off) then all his past sins will be forgiven."
قَالَ رَسُولُ اللَّهِ ﷺ مَنْ يَقُمْ لَيْلَةَ الْقَدْرِ إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ
Messenger of Allah ﷺ said, "Whoever establishes the prayers on the night of Qadr out of sincere faith and hoping to attain Allah's rewards (not to show off) then all his past sins will be forgiven." (Using translation from Bukhārī 35)
قَالَ رَسُولُ اللهِ ﷺ «مَنْ يَقُمْ لَيْلَةَ الْقَدْرِ إِيمَانًا وَاحْتِسَابًا يَغْفِرُ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ»
"مَنْ يَقُمْ لَيلَةَ الْقَدْرِ فَيُوَافِيهَا إِيمَانًا وَاحْتِسَابًا، يُغْفَرْ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ".