Riyad as-Salihin 1189
Abu Hurairah (May Allah be pleased with him) reported:
The Prophet (ﷺ) said, "Whosoever performs Qiyam during Lailat-ul-Qadr (Night of Decree), with Faith and being hopeful of Allah's reward, will have his former sins forgiven." [Al-Bukhari and Muslim] .
وعن أبي هريرة رضي الله عنه، عن النبي صلى الله عليه وسلم قال‏:‏ ‏
"‏من قام ليلة القدر إيمانا واحتسابًا غفر له ما تقدم من ذنبه‏"‏‏.‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏ ‏.‏