Hadith on Night Prayer: The virtue of night prayer in the month of Ramadan

Abu Huraira reported: The Messenger of Allah, peace be upon him, would encourage standing for night prayer in the month of Ramadan without making it an obligation, and he would say, “Whoever stands in the night prayer during Ramadan out of faith and seeking his reward, then all of his previous sins will be forgiven.” When the Messenger of Allah died, this became a regular practice and continued throughout the Caliphate of Abu Baker and Umar.

[Sahih Muslim, Book 4, Number 1663]

عَنْ أَبِي هُرَيْرَةَ قَالَ كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يُرَغِّبُ فِي قِيَامِ رَمَضَانَ مِنْ غَيْرِ أَنْ يَأْمُرَهُمْ فِيهِ بِعَزِيمَةٍ فَيَقُولُ مَنْ قَامَ رَمَضَانَ إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ مَا تَقَدَّمَ مِنْ ذَنْبِهِ فَتُوُفِّيَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَالْأَمْرُ عَلَى ذَلِكَ ثُمَّ كَانَ الْأَمْرُ عَلَى ذَلِكَ فِي خِلَافَةِ أَبِي بَكْرٍ وَصَدْرًا مِنْ خِلَافَةِ عُمَرَ عَلَى ذَلِكَ

صحيح مسلم  كتاب صلاة المسافرين وقصرها  باب الترغيب في قيام رمضان وهو التراويح