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].
App reference: Book 9, Hadith 199
Arabic/English book reference: Book 9, Hadith 1189