Abu Hurairah narrated:"The Messenger of Allah would encourage the night prayer in Ramadan without firmly ordering it, and he would say: "Whoever stands (in the night prayer) for Ramadan with faith and seeking the reward (from Allah), then he will be forgiven what has preceded of his sins.' So the Messenger of Allah died and the matter was like that. Then the matter was the same during the Khilafah of Abu Bakr and it continued during a portion of the Khilafah of Umar bin Al-Khattab

English translation · Jami' at-Tirmidhi