Narrated Abu Hurairah:
The Messenger of Allah ﷺ used to commend prayer at night during Ramadan, but did not command it as duty. He would say: If anyone prays during the night in Ramadan because of faith and seeking his reward from Allah, his previous sins will be forgiven for him. When the Messenger of Allah ﷺ died, this was the practice, and it continued thus during Abu Bakr's caliphate and early part of 'Umar's.

Abu Dawud said: This tradition has been transmitted by 'Uqail, Yunus, and Abu Uwais in like manner. The version of 'Uqail goes: He who fasts during Ramadan and prays during the night.

حَدَّثَنَا الْحَسَنُ بْنُ عَلِيٍّ، وَمُحَمَّدُ بْنُ الْمُتَوَكِّلِ، قَالاَ حَدَّثَنَا عَبْدُ الرَّزَّاقِ، أَخْبَرَنَا مَعْمَرٌ، - قَالَ الْحَسَنُ فِي حَدِيثِهِ وَمَالِكُ بْنُ أَنَسٍ - عَنِ الزُّهْرِيِّ، عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي هُرَيْرَةَ، قَالَ كَانَ رَسُولُ اللَّهِ ﷺ يُرَغِّبُ فِي قِيَامِ رَمَضَانَ مِنْ غَيْرِ أَنْ يَأْمُرَهُمْ بِعَزِيمَةٍ ثُمَّ يَقُولُ " مَنْ قَامَ رَمَضَانَ إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ " . فَتُوُفِّيَ رَسُولُ اللَّهِ ﷺ وَالأَمْرُ عَلَى ذَلِكَ ثُمَّ كَانَ الأَمْرُ عَلَى ذَلِكَ فِي خِلاَفَةِ أَبِي بَكْرٍ - رضى الله عنه - وَصَدْرًا مِنْ خِلاَفَةِ عُمَرَ رضى الله عنه . قَالَ أَبُو دَاوُدَ وَكَذَا رَوَاهُ عُقَيْلٌ وَيُونُسُ وَأَبُو أُوَيْسٍ " مَنْ قَامَ رَمَضَانَ " . وَرَوَى عُقَيْلٌ " مَنْ صَامَ رَمَضَانَ وَقَامَهُ " .