Sahih Muslim 1779
صحيح مسلم#1779SahihAbu Huraira reported Allah's Messenger (ﷺ) as saying:He who observed prayer at night during Ramadan, because of faith and seeking his reward from Allah, 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: 6:207