Sahih Muslim 1781
صحيح مسلم#1781SahihAbu Huraira reported Allah's Messenger (ﷺ) as saying:He who observed the fasts of Ramadan with faith and seeking reward (from Allah), all his previous sins would be forgiven, and he who observed prayer on Lailat-ul- Qadr with faith and seeking reward (from Allah), all his previous sins would be forgiven
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 6:209