It wasnarrated that Abu Hurairah said:
"The Messenger of Allah (ﷺ)said: 'Whoever fasts Ramadan and spends its nights in prayer, outoffaith and in hope of reward, his previous sins will be forgiven.'" (JA)
English reference (JA): Vol. 1, Book 5, Hadith 1326 (JA)
Arabic reference (JA): Book 5, Hadith 1387 (JA)