Sahih Muslim · Hadith 1815

حدثنا يحيى بن يحيى، قال قرأت على مالك عن ابن شهاب، عن حميد بن عبد الرحمن، عن أبي هريرة، أن رسول الله صلى الله عليه وسلم قال ‏"‏ من قام رمضان إيمانا واحتسابا غفر له ما تقدم من ذنبه ‏"‏ ‏.‏

Abu Huraira reported: The Messenger of Allah (may peace be upon him) used to exhort (his Companions) to pray (at night) during Ramadan without commanding them to observe it as an obligatory act, and say: He who observed the night prayer in Ramadan because of faith and seeking his reward (from Allah), all his previous sins would be forgiven. When Allah's Messenger (may peace be upon him) died, this was the practice, and it continued thus during Abu Bakr's caliphate and the early part of 'Umar's caliphate.

Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).