كتاب صلاة المسافرين وقصرها
6
The Book of Prayer - Travellers
(25)
Chapter: Encouragement to pray qiyam during Ramadan, which is Tarawih
(25)
باب التَّرْغِيبِ فِي قِيَامِ رَمَضَانَ وَهُوَ التَّرَاوِيحُ ‏
Sahih Muslim 760 b

Abu Huraira reported Allah's Apostle (ﷺ) as saying:

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.
حَدَّثَنِي مُحَمَّدُ بْنُ رَافِعٍ، حَدَّثَنَا شَبَابَةُ، حَدَّثَنِي وَرْقَاءُ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏ "‏ مَنْ يَقُمْ لَيْلَةَ الْقَدْرِ فَيُوَافِقُهَا - أُرَاهُ قَالَ - إِيمَانًا وَاحْتِسَابًا غُفِرَ لَهُ ‏"‏ ‏.‏
Reference : Sahih Muslim 760 b
In-book reference : Book 6, Hadith 210
USC-MSA web (English) reference : Book 4, Hadith 1665
  (deprecated numbering scheme)